std.datetime.interval - D Programming Language
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# std.datetime.interval

Category | Functions
--- | ---
Main types | Interval Direction
Special intervals | everyDayOfWeek everyMonth everyDuration
Special intervals | NegInfInterval PosInfInterval
Underlying ranges | IntervalRange NegInfIntervalRange PosInfIntervalRange
Flags | PopFirst

License:
Boost License 1.0.
Authors:
Jonathan M Davis

Source std/datetime/interval.d

enum `Direction`: int;
  Indicates a direction in time. One example of its use is Interval's expand function which uses it to indicate whether the interval should be expanded backwards (into the past), forwards (into the future), or both.
  `bwd`
    Backward.
  `fwd`
    Forward.
  `both`
    Both backward and forward.
alias `PopFirst` = std.typecons.Flag!"popFirst".Flag;
  Used to indicate whether popFront should be called immediately upon creating a range. The idea is that for some functions used to generate a range for an interval, front is not necessarily a time point which would ever be generated by the range (e.g. if the range were every Sunday within an interval, but the interval started on a Monday), so there needs to be a way to deal with that. To get the first time point in the range to match what the function generates, then use `PopFirst`.yes to indicate that the range should have popFront called on it before the range is returned so that front is a time point which the function would generate. To let the first time point not match the generator function, use PopFront.no.
  For instance, if the function used to generate a range of time points generated successive Easters (i.e. you're iterating over all of the Easters within the interval), the initial date probably isn't an Easter. Using `PopFirst`.yes would tell the function which returned the range that popFront was to be called so that front would then be an Easter - the next one generated by the function (which when iterating forward would be the Easter following the original front, while when iterating backward, it would be the Easter prior to the original front). If `PopFirst`.no were used, then front would remain the original time point and it would not necessarily be a time point which would be generated by the range-generating function (which in many cases is exactly what is desired - e.g. if iterating over every day starting at the beginning of the interval).
  If set to `PopFirst`.no, then popFront is not called before returning the range.
  Otherwise, if set to `PopFirst`.yes, then popFront is called before returning the range.
struct `Interval`(TP);
  Represents an interval of time.
  An `Interval` has a starting point and an end point. The interval of time is therefore the time starting at the starting point up to, but not including, the end point. e.g.

  [January 5th, 2010 - March 10th, 2010)
  [05:00:30 - 12:00:00)
  [1982-01-04T08:59:00 - 2010-07-04T12:00:00)

  A range can be obtained from an `Interval`, allowing iteration over that interval, with the exact time points which are iterated over depending on the function which generates the range.
  pure this(U)(scope const TP `begin`, scope const U `end`)
  if (is(immutable(TP) == immutable(U)));
    Parameters:

    TP `begin` | The time point which begins the interval.
    U `end` | The time point which ends (but is not included in) the interval.

    Throws:
    std.datetime.date.DateTimeException if end is before begin.

    Example

        Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));

  pure this(D)(scope const TP `begin`, scope const D `duration`)
  if (__traits(compiles, `begin` + `duration`));
    Parameters:

    TP `begin` | The time point which begins the interval.
    D `duration` | The duration from the starting point to the end point.

    Throws:
    std.datetime.date.DateTimeException if the resulting end is before `begin`.

    Example

        assert(Interval!Date(Date(1996, 1, 2), dur!"days"(3)) ==
               Interval!Date(Date(1996, 1, 2), Date(1996, 1, 5)));

  pure nothrow ref Interval `opAssign`(const ref Interval `rhs`);
    Parameters:

    Interval `rhs` | The Interval to assign to this one.

  pure nothrow ref Interval `opAssign`(Interval `rhs`);
    Parameters:

    Interval `rhs` | The Interval to assign to this one.

  const pure nothrow @property TP `begin`();
    The starting point of the interval. It is included in the interval.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).begin ==
               Date(1996, 1, 2));

  pure @property void `begin`(TP `timePoint`);
    The starting point of the interval. It is included in the interval.
    Parameters:

    TP `timePoint` | The time point to set `begin` to.

    Throws:
    std.datetime.date.DateTimeException if the resulting interval would be invalid.
  const pure nothrow @property TP `end`();
    The end point of the interval. It is excluded from the interval.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).end ==
               Date(2012, 3, 1));

  pure @property void `end`(TP `timePoint`);
    The end point of the interval. It is excluded from the interval.
    Parameters:

    TP `timePoint` | The time point to set end to.

    Throws:
    std.datetime.date.DateTimeException if the resulting interval would be invalid.
  const pure nothrow @property auto `length`();
    Returns the duration between begin and end.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).length ==
               dur!"days"(5903));

  const pure nothrow @property bool `empty`();
    Whether the interval's length is 0, that is, whether begin == end.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(1996, 1, 2)).empty);
        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).empty);

  const pure bool `contains`(scope const TP `timePoint`);
    Whether the given time point is within this interval.
    Parameters:

    TP `timePoint` | The time point to check for inclusion in this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    Date(1994, 12, 24)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    Date(2000, 1, 5)));
        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    Date(2012, 3, 1)));

  const pure bool `contains`(scope const Interval `interval`);
    Whether the given interval is completely within this interval.
    Parameters:

    Interval `interval` | The interval to check for inclusion in this interval.

    Throws:
    std.datetime.date.DateTimeException if either interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    Interval!Date(Date(1998, 2, 28), Date(2013, 5, 1))));

  const pure bool `contains`(scope const PosInfInterval!TP `interval`);
    Whether the given interval is completely within this interval.
    Always returns false (unless this interval is empty), because an interval going to positive infinity can never be contained in a finite interval.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check for inclusion in this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    PosInfInterval!Date(Date(1999, 5, 4))));

  const pure bool `contains`(scope const NegInfInterval!TP `interval`);
    Whether the given interval is completely within this interval.
    Always returns false (unless this interval is empty), because an interval beginning at negative infinity can never be contained in a finite interval.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for inclusion in this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).contains(
                    NegInfInterval!Date(Date(1996, 5, 4))));

  const pure bool `isBefore`(scope const TP `timePoint`);
    Whether this interval is before the given time point.
    Parameters:

    TP `timePoint` | The time point to check whether this interval is before it.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    Date(1994, 12, 24)));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    Date(2000, 1, 5)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    Date(2012, 3, 1)));

  const pure bool `isBefore`(scope const Interval `interval`);
    Whether this interval is before the given interval and does not intersect with it.
    Parameters:

    Interval `interval` | The interval to check for against this interval.

    Throws:
    std.datetime.date.DateTimeException if either interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    Interval!Date(Date(2012, 3, 1), Date(2013, 5, 1))));

  const pure bool `isBefore`(scope const PosInfInterval!TP `interval`);
    Whether this interval is before the given interval and does not intersect with it.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check for against this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    PosInfInterval!Date(Date(2013, 3, 7))));

  const pure bool `isBefore`(scope const NegInfInterval!TP `interval`);
    Whether this interval is before the given interval and does not intersect with it.
    Always returns false (unless this interval is empty) because a finite interval can never be before an interval beginning at negative infinity.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for against this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isBefore(
                    NegInfInterval!Date(Date(1996, 5, 4))));

  const pure bool `isAfter`(scope const TP `timePoint`);
    Whether this interval is after the given time point.
    Parameters:

    TP `timePoint` | The time point to check whether this interval is after it.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    Date(1994, 12, 24)));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    Date(2000, 1, 5)));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    Date(2012, 3, 1)));

  const pure bool `isAfter`(scope const Interval `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Parameters:

    Interval `interval` | The interval to check against this interval.

    Throws:
    std.datetime.date.DateTimeException if either interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    Interval!Date(Date(1989, 3, 1), Date(1996, 1, 2))));

  const pure bool `isAfter`(scope const PosInfInterval!TP `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Always returns false (unless this interval is empty) because a finite interval can never be after an interval going to positive infinity.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check against this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    PosInfInterval!Date(Date(1999, 5, 4))));

  const pure bool `isAfter`(scope const NegInfInterval!TP `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check against this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAfter(
                    NegInfInterval!Date(Date(1996, 1, 2))));

  const pure bool `intersects`(scope const Interval `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    Interval `interval` | The interval to check for intersection with this interval.

    Throws:
    std.datetime.date.DateTimeException if either interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    Interval!Date(Date(1989, 3, 1), Date(1996, 1, 2))));

  const pure bool `intersects`(scope const PosInfInterval!TP `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check for intersection with this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    PosInfInterval!Date(Date(2012, 3, 1))));

  const pure bool `intersects`(scope const NegInfInterval!TP `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for intersection with this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    NegInfInterval!Date(Date(1996, 1, 2))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersects(
                    NegInfInterval!Date(Date(2000, 1, 2))));

  const Interval `intersection`(scope const Interval `interval`);
    Returns the intersection of two intervals
    Parameters:

    Interval `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect or if either interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersection(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2000, 8, 2)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersection(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))) ==
               Interval!Date(Date(1999, 1 , 12), Date(2011, 9, 17)));

  const Interval `intersection`(scope const PosInfInterval!TP `interval`);
    Returns the intersection of two intervals
    Parameters:

    PosInfInterval!TP `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect or if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersection(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2012, 3, 1)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersection(
                    PosInfInterval!Date(Date(1999, 1, 12))) ==
               Interval!Date(Date(1999, 1 , 12), Date(2012, 3, 1)));

  const Interval `intersection`(scope const NegInfInterval!TP `interval`);
    Returns the intersection of two intervals
    Parameters:

    NegInfInterval!TP `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect or if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersection(
                    NegInfInterval!Date(Date(1999, 7, 6))) ==
               Interval!Date(Date(1996, 1 , 2), Date(1999, 7, 6)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).intersection(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2012, 3, 1)));

  const pure bool `isAdjacent`(scope const Interval `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    Interval `interval` | The interval to check whether its adjecent to this interval.

    Throws:
    std.datetime.date.DateTimeException if either interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(1990, 7, 6), Date(1996, 1, 2))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(2012, 3, 1), Date(2013, 9, 17))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(1989, 3, 1), Date(2012, 3, 1))));

  const pure bool `isAdjacent`(scope const PosInfInterval!TP `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check whether its adjecent to this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    PosInfInterval!Date(Date(2012, 3, 1))));

  const pure bool `isAdjacent`(scope const NegInfInterval!TP `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check whether its adjecent to this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    NegInfInterval!Date(Date(1996, 1, 2))));

        assert(!Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).isAdjacent(
                    NegInfInterval!Date(Date(2000, 1, 2))));

  const Interval `merge`(scope const Interval `interval`);
    Returns the union of two intervals
    Parameters:

    Interval `interval` | The interval to merge with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect and are not adjacent or if either interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).merge(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               Interval!Date(Date(1990, 7 , 6), Date(2012, 3, 1)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).merge(
                    Interval!Date(Date(2012, 3, 1), Date(2013, 5, 7))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2013, 5, 7)));

  const PosInfInterval!TP `merge`(scope const PosInfInterval!TP `interval`);
    Returns the union of two intervals
    Parameters:

    PosInfInterval!TP `interval` | The interval to merge with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect and are not adjacent or if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).merge(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               PosInfInterval!Date(Date(1990, 7 , 6)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).merge(
                    PosInfInterval!Date(Date(2012, 3, 1))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

  const NegInfInterval!TP `merge`(scope const NegInfInterval!TP `interval`);
    Returns the union of two intervals
    Parameters:

    NegInfInterval!TP `interval` | The interval to merge with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect and are not adjacent or if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).merge(
                    NegInfInterval!Date(Date(1996, 1, 2))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).merge(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               NegInfInterval!Date(Date(2013, 1 , 12)));

  const pure Interval `span`(scope const Interval `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    Interval `interval` | The interval to create a span together with this interval.

    Throws:
    std.datetime.date.DateTimeException if either interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).span(
                    Interval!Date(Date(1990, 7, 6), Date(1991, 1, 8))) ==
               Interval!Date(Date(1990, 7 , 6), Date(2012, 3, 1)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).span(
                    Interval!Date(Date(2012, 3, 1), Date(2013, 5, 7))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2013, 5, 7)));

  const pure PosInfInterval!TP `span`(scope const PosInfInterval!TP `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    PosInfInterval!TP `interval` | The interval to create a span together with this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).span(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               PosInfInterval!Date(Date(1990, 7 , 6)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).span(
                    PosInfInterval!Date(Date(2050, 1, 1))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

  const pure NegInfInterval!TP `span`(scope const NegInfInterval!TP `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    NegInfInterval!TP `interval` | The interval to create a span together with this interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Example

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).span(
                    NegInfInterval!Date(Date(1602, 5, 21))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

        assert(Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)).span(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               NegInfInterval!Date(Date(2013, 1 , 12)));

  pure void `shift`(D)(D `duration`)
  if (__traits(compiles, begin + `duration`));
    Shifts the interval forward or backwards in time by the given duration (a positive duration shifts the interval forward; a negative duration shifts it backward). Effectively, it does begin += duration and end += duration.
    Parameters:

    D `duration` | The duration to shift the interval by.

    Throws:
    std.datetime.date.DateTimeException this interval is empty or if the resulting interval would be invalid.

    Example

        auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 4, 5));
        auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 4, 5));

        interval1.shift(dur!"days"(50));
        assert(interval1 == Interval!Date(Date(1996, 2, 21), Date(2012, 5, 25)));

        interval2.shift(dur!"days"(-50));
        assert(interval2 == Interval!Date(Date(1995, 11, 13), Date(2012, 2, 15)));

  void `shift`(T)(T `years`, T `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (isIntegral!T);
    Shifts the interval forward or backwards in time by the given number of years and/or months (a positive number of years and months shifts the interval forward; a negative number shifts it backward). It adds the years the given years and months to both begin and end. It effectively calls add!"`years`"() and then add!"`months`"() on begin and end with the given number of years and months.
    Parameters:

    T `years` | The number of years to shift the interval by.
    T `months` | The number of months to shift the interval by.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on begin and end, causing their month to increment.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty or if the resulting interval would be invalid.

    Example

        auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));
        auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));

        interval1.shift(2);
        assert(interval1 == Interval!Date(Date(1998, 1, 2), Date(2014, 3, 1)));

        interval2.shift(-2);
        assert(interval2 == Interval!Date(Date(1994, 1, 2), Date(2010, 3, 1)));

  pure void `expand`(D)(D `duration`, Direction `dir` = Direction.both)
  if (__traits(compiles, begin + `duration`));
    Expands the interval forwards and/or backwards in time. Effectively, it does begin -= duration and/or end += duration. Whether it expands forwards and/or backwards in time is determined by dir.
    Parameters:

    D `duration` | The duration to expand the interval by.
    Direction `dir` | The direction in time to expand the interval.

    Throws:
    std.datetime.date.DateTimeException this interval is empty or if the resulting interval would be invalid.

    Example

        auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));
        auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));

        interval1.expand(2);
        assert(interval1 == Interval!Date(Date(1994, 1, 2), Date(2014, 3, 1)));

        interval2.expand(-2);
        assert(interval2 == Interval!Date(Date(1998, 1, 2), Date(2010, 3, 1)));

  void `expand`(T)(T `years`, T `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes, Direction `dir` = Direction.both)
  if (isIntegral!T);
    Expands the interval forwards and/or backwards in time. Effectively, it subtracts the given number of months/years from begin and adds them to end. Whether it expands forwards and/or backwards in time is determined by dir.
    Parameters:

    T `years` | The number of years to expand the interval by.
    T `months` | The number of months to expand the interval by.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on begin and end, causing their month to increment.
    Direction `dir` | The direction in time to expand the interval.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty or if the resulting interval would be invalid.

    Example

        auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));
        auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));

        interval1.expand(2);
        assert(interval1 == Interval!Date(Date(1994, 1, 2), Date(2014, 3, 1)));

        interval2.expand(-2);
        assert(interval2 == Interval!Date(Date(1998, 1, 2), Date(2010, 3, 1)));

  const IntervalRange!(TP, Direction.fwd) `fwdRange`(TP delegate(scope const TP) `func`, PopFirst `popFirst` = PopFirst.no);
    Returns a range which iterates forward over the interval, starting at begin, using func to generate each successive time point.
    The range's front is the interval's begin. func is used to generate the next front when popFront is called. If popFirst is PopFirst.yes, then popFront is called before the range is returned (so that front is a time point which func would generate).
    If func ever generates a time point less than or equal to the current front of the range, then a std.datetime.date.DateTimeException will be thrown. The range will be empty and iteration complete when func generates a time point equal to or beyond the end of the interval.
    There are helper functions in this module which generate common delegates to pass to `fwdRange`. Their documentation starts with "Range-generating function," making them easily searchable.
    Parameters:

    TP delegate(scope const TP) `func` | The function used to generate the time points of the range over the interval.
    PopFirst `popFirst` | Whether popFront should be called on the range before returning it.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Warning func must be logically pure. Ideally, func would be a function pointer to a pure function, but forcing func to be pure is far too restrictive to be useful, and in order to have the ease of use of having functions which generate functions to pass to `fwdRange`, func must be a delegate.

    If func retains state which changes as it is called, then some algorithms will not work correctly, because the range's save will have failed to have really saved the range's state. To avoid such bugs, don't pass a delegate which is not logically pure to `fwdRange`. If func is given the same time point with two different calls, it must return the same result both times.
    Of course, none of the functions in this module have this problem, so it's only relevant if when creating a custom delegate.

    Example

        auto interval = Interval!Date(Date(2010, 9, 1), Date(2010, 9, 9));
        auto func = delegate (scope const Date date) // For iterating over even-numbered days.
                    {
                        if ((date.day & 1) == 0)
                            return date + dur!"days"(2);

                        return date + dur!"days"(1);
                    };
        auto range = interval.fwdRange(func);

        // An odd day. Using PopFirst.yes would have made this Date(2010, 9, 2).
        assert(range.front == Date(2010, 9, 1));

        range.popFront();
        assert(range.front == Date(2010, 9, 2));

        range.popFront();
        assert(range.front == Date(2010, 9, 4));

        range.popFront();
        assert(range.front == Date(2010, 9, 6));

        range.popFront();
        assert(range.front == Date(2010, 9, 8));

        range.popFront();
        assert(range.empty);

  const IntervalRange!(TP, Direction.bwd) `bwdRange`(TP delegate(scope const TP) `func`, PopFirst `popFirst` = PopFirst.no);
    Returns a range which iterates backwards over the interval, starting at end, using func to generate each successive time point.
    The range's front is the interval's end. func is used to generate the next front when popFront is called. If popFirst is PopFirst.yes, then popFront is called before the range is returned (so that front is a time point which func would generate).
    If func ever generates a time point greater than or equal to the current front of the range, then a std.datetime.date.DateTimeException will be thrown. The range will be empty and iteration complete when func generates a time point equal to or less than the begin of the interval.
    There are helper functions in this module which generate common delegates to pass to `bwdRange`. Their documentation starts with "Range-generating function," making them easily searchable.
    Parameters:

    TP delegate(scope const TP) `func` | The function used to generate the time points of the range over the interval.
    PopFirst `popFirst` | Whether popFront should be called on the range before returning it.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Warning func must be logically pure. Ideally, func would be a function pointer to a pure function, but forcing func to be pure is far too restrictive to be useful, and in order to have the ease of use of having functions which generate functions to pass to fwdRange, func must be a delegate.

    If func retains state which changes as it is called, then some algorithms will not work correctly, because the range's save will have failed to have really saved the range's state. To avoid such bugs, don't pass a delegate which is not logically pure to fwdRange. If func is given the same time point with two different calls, it must return the same result both times.
    Of course, none of the functions in this module have this problem, so it's only relevant for custom delegates.

    Example

        auto interval = Interval!Date(Date(2010, 9, 1), Date(2010, 9, 9));
        auto func = delegate (scope const Date date) // For iterating over even-numbered days.
                    {
                        if ((date.day & 1) == 0)
                            return date - dur!"days"(2);

                        return date - dur!"days"(1);
                    };
        auto range = interval.bwdRange(func);

        // An odd day. Using PopFirst.yes would have made this Date(2010, 9, 8).
        assert(range.front == Date(2010, 9, 9));

        range.popFront();
        assert(range.front == Date(2010, 9, 8));

        range.popFront();
        assert(range.front == Date(2010, 9, 6));

        range.popFront();
        assert(range.front == Date(2010, 9, 4));

        range.popFront();
        assert(range.front == Date(2010, 9, 2));

        range.popFront();
        assert(range.empty);

  const nothrow @safe string `toString`();
  const void `toString`(Writer)(ref Writer `w`)
  if (isOutputRange!(Writer, char));
    Converts this interval to a string.
    Parameters:

    Writer `w` | A char accepting output range

    Returns:
    A string when not using an output range; void otherwise.
struct `PosInfInterval`(TP);
  Represents an interval of time which has positive infinity as its end point.
  Any ranges which iterate over a `PosInfInterval` are infinite. So, the main purpose of using `PosInfInterval` is to create an infinite range which starts at a fixed point in time and goes to positive infinity.
  pure nothrow this(scope const TP `begin`);
    Parameters:

    TP `begin` | The time point which begins the interval.

    Example

        auto interval = PosInfInterval!Date(Date(1996, 1, 2));

  pure nothrow ref PosInfInterval `opAssign`(const ref PosInfInterval `rhs`);
    Parameters:

    PosInfInterval `rhs` | The PosInfInterval to assign to this one.

  pure nothrow ref PosInfInterval `opAssign`(PosInfInterval `rhs`);
    Parameters:

    PosInfInterval `rhs` | The PosInfInterval to assign to this one.

  const pure nothrow @property TP `begin`();
    The starting point of the interval. It is included in the interval.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).begin == Date(1996, 1, 2));

  pure nothrow @property void `begin`(TP `timePoint`);
    The starting point of the interval. It is included in the interval.
    Parameters:

    TP `timePoint` | The time point to set `begin` to.

  enum bool `empty`;
    Whether the interval's length is 0. Always returns false.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).empty);

  const pure nothrow bool `contains`(TP `timePoint`);
    Whether the given time point is within this interval.
    Parameters:

    TP `timePoint` | The time point to check for inclusion in this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).contains(Date(1994, 12, 24)));
        assert(PosInfInterval!Date(Date(1996, 1, 2)).contains(Date(2000, 1, 5)));

  const pure bool `contains`(scope const Interval!TP `interval`);
    Whether the given interval is completely within this interval.
    Parameters:

    Interval!TP `interval` | The interval to check for inclusion in this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).contains(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).contains(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).contains(
                    Interval!Date(Date(1998, 2, 28), Date(2013, 5, 1))));

  const pure nothrow bool `contains`(scope const PosInfInterval `interval`);
    Whether the given interval is completely within this interval.
    Parameters:

    PosInfInterval `interval` | The interval to check for inclusion in this interval.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).contains(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).contains(
                    PosInfInterval!Date(Date(1995, 7, 2))));

  const pure nothrow bool `contains`(scope const NegInfInterval!TP `interval`);
    Whether the given interval is completely within this interval.
    Always returns false because an interval going to positive infinity can never contain an interval beginning at negative infinity.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for inclusion in this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).contains(
                    NegInfInterval!Date(Date(1996, 5, 4))));

  const pure nothrow bool `isBefore`(scope const TP `timePoint`);
    Whether this interval is before the given time point.
    Always returns false because an interval going to positive infinity can never be before any time point.
    Parameters:

    TP `timePoint` | The time point to check whether this interval is before it.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(Date(1994, 12, 24)));
        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(Date(2000, 1, 5)));

  const pure bool `isBefore`(scope const Interval!TP `interval`);
    Whether this interval is before the given interval and does not intersect it.
    Always returns false (unless the given interval is empty) because an interval going to positive infinity can never be before any other interval.
    Parameters:

    Interval!TP `interval` | The interval to check for against this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

  const pure nothrow bool `isBefore`(scope const PosInfInterval `interval`);
    Whether this interval is before the given interval and does not intersect it.
    Always returns false because an interval going to positive infinity can never be before any other interval.
    Parameters:

    PosInfInterval `interval` | The interval to check for against this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(
                    PosInfInterval!Date(Date(1992, 5, 4))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(
                    PosInfInterval!Date(Date(2013, 3, 7))));

  const pure nothrow bool `isBefore`(scope const NegInfInterval!TP `interval`);
    Whether this interval is before the given interval and does not intersect it.
    Always returns false because an interval going to positive infinity can never be before any other interval.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for against this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isBefore(
                    NegInfInterval!Date(Date(1996, 5, 4))));

  const pure nothrow bool `isAfter`(scope const TP `timePoint`);
    Whether this interval is after the given time point.
    Parameters:

    TP `timePoint` | The time point to check whether this interval is after it.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).isAfter(Date(1994, 12, 24)));
        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAfter(Date(2000, 1, 5)));

  const pure bool `isAfter`(scope const Interval!TP `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Parameters:

    Interval!TP `interval` | The interval to check against this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    Interval!Date(Date(1989, 3, 1), Date(1996, 1, 2))));

  const pure nothrow bool `isAfter`(scope const PosInfInterval `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Always returns false because an interval going to positive infinity can never be after another interval going to positive infinity.
    Parameters:

    PosInfInterval `interval` | The interval to check against this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    PosInfInterval!Date(Date(1990, 1, 7))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    PosInfInterval!Date(Date(1999, 5, 4))));

  const pure nothrow bool `isAfter`(scope const NegInfInterval!TP `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check against this interval.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    NegInfInterval!Date(Date(1996, 1, 2))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAfter(
                    NegInfInterval!Date(Date(2000, 7, 1))));

  const pure bool `intersects`(scope const Interval!TP `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    Interval!TP `interval` | The interval to check for intersection with this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    Interval!Date(Date(1989, 3, 1), Date(1996, 1, 2))));

  const pure nothrow bool `intersects`(scope const PosInfInterval `interval`);
    Whether the given interval overlaps this interval.
    Always returns true because two intervals going to positive infinity always overlap.
    Parameters:

    PosInfInterval `interval` | The interval to check for intersection with this interval.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    PosInfInterval!Date(Date(1990, 1, 7))));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    PosInfInterval!Date(Date(1999, 5, 4))));

  const pure nothrow bool `intersects`(scope const NegInfInterval!TP `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for intersection with this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    NegInfInterval!Date(Date(1996, 1, 2))));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersects(
                    NegInfInterval!Date(Date(2000, 7, 1))));

  const Interval!TP `intersection`(scope const Interval!TP `interval`);
    Returns the intersection of two intervals
    Parameters:

    Interval!TP `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect or if the given interval is empty.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersection(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2000, 8, 2)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersection(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))) ==
               Interval!Date(Date(1999, 1 , 12), Date(2011, 9, 17)));

  const pure nothrow PosInfInterval `intersection`(scope const PosInfInterval `interval`);
    Returns the intersection of two intervals
    Parameters:

    PosInfInterval `interval` | The interval to intersect with this interval.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersection(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersection(
                    PosInfInterval!Date(Date(1999, 1, 12))) ==
               PosInfInterval!Date(Date(1999, 1 , 12)));

  const Interval!TP `intersection`(scope const NegInfInterval!TP `interval`);
    Returns the intersection of two intervals
    Parameters:

    NegInfInterval!TP `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersection(
                    NegInfInterval!Date(Date(1999, 7, 6))) ==
               Interval!Date(Date(1996, 1 , 2), Date(1999, 7, 6)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).intersection(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               Interval!Date(Date(1996, 1 , 2), Date(2013, 1, 12)));

  const pure bool `isAdjacent`(scope const Interval!TP `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    Interval!TP `interval` | The interval to check whether its adjecent to this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).isAdjacent(
                    Interval!Date(Date(1989, 3, 1), Date(1996, 1, 2))));

        assert(!PosInfInterval!Date(Date(1999, 1, 12)).isAdjacent(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

  const pure nothrow bool `isAdjacent`(scope const PosInfInterval `interval`);
    Whether the given interval is adjacent to this interval.
    Always returns false because two intervals going to positive infinity can never be adjacent to one another.
    Parameters:

    PosInfInterval `interval` | The interval to check whether its adjecent to this interval.

    Example

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAdjacent(
                    PosInfInterval!Date(Date(1990, 1, 7))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAdjacent(
                    PosInfInterval!Date(Date(1996, 1, 2))));

  const pure nothrow bool `isAdjacent`(scope const NegInfInterval!TP `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check whether its adjecent to this interval.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).isAdjacent(
                    NegInfInterval!Date(Date(1996, 1, 2))));

        assert(!PosInfInterval!Date(Date(1996, 1, 2)).isAdjacent(
                    NegInfInterval!Date(Date(2000, 7, 1))));

  const PosInfInterval `merge`(scope const Interval!TP `interval`);
    Returns the union of two intervals
    Parameters:

    Interval!TP `interval` | The interval to merge with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect and are not adjacent or if the given interval is empty.

    Note There is no overload for `merge` which takes a NegInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).merge(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               PosInfInterval!Date(Date(1990, 7 , 6)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).merge(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

  const pure nothrow PosInfInterval `merge`(scope const PosInfInterval `interval`);
    Returns the union of two intervals
    Parameters:

    PosInfInterval `interval` | The interval to merge with this interval.

    Note There is no overload for `merge` which takes a NegInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).merge(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               PosInfInterval!Date(Date(1990, 7 , 6)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).merge(
                    PosInfInterval!Date(Date(1999, 1, 12))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

  const pure PosInfInterval `span`(scope const Interval!TP `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    Interval!TP `interval` | The interval to create a span together with this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Note There is no overload for `span` which takes a NegInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).span(
                    Interval!Date(Date(500, 8, 9), Date(1602, 1, 31))) ==
               PosInfInterval!Date(Date(500, 8, 9)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).span(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               PosInfInterval!Date(Date(1990, 7 , 6)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).span(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

  const pure nothrow PosInfInterval `span`(scope const PosInfInterval `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    PosInfInterval `interval` | The interval to create a span together with this interval.

    Note There is no overload for `span` which takes a NegInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(PosInfInterval!Date(Date(1996, 1, 2)).span(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               PosInfInterval!Date(Date(1990, 7 , 6)));

        assert(PosInfInterval!Date(Date(1996, 1, 2)).span(
                    PosInfInterval!Date(Date(1999, 1, 12))) ==
               PosInfInterval!Date(Date(1996, 1 , 2)));

  pure nothrow void `shift`(D)(D `duration`)
  if (__traits(compiles, begin + `duration`));
    Shifts the begin of this interval forward or backwards in time by the given duration (a positive duration shifts the interval forward; a negative duration shifts it backward). Effectively, it does begin += duration.
    Parameters:

    D `duration` | The duration to shift the interval by.

    Example

        auto interval1 = PosInfInterval!Date(Date(1996, 1, 2));
        auto interval2 = PosInfInterval!Date(Date(1996, 1, 2));

        interval1.shift(dur!"days"(50));
        assert(interval1 == PosInfInterval!Date(Date(1996, 2, 21)));

        interval2.shift(dur!"days"(-50));
        assert(interval2 == PosInfInterval!Date(Date(1995, 11, 13)));

  void `shift`(T)(T `years`, T `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (isIntegral!T);
    Shifts the begin of this interval forward or backwards in time by the given number of years and/or months (a positive number of years and months shifts the interval forward; a negative number shifts it backward). It adds the years the given years and months to begin. It effectively calls add!"`years`"() and then add!"`months`"() on begin with the given number of years and months.
    Parameters:

    T `years` | The number of years to shift the interval by.
    T `months` | The number of months to shift the interval by.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on begin, causing its month to increment.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty or if the resulting interval would be invalid.

    Example

        auto interval1 = PosInfInterval!Date(Date(1996, 1, 2));
        auto interval2 = PosInfInterval!Date(Date(1996, 1, 2));

        interval1.shift(dur!"days"(50));
        assert(interval1 == PosInfInterval!Date(Date(1996, 2, 21)));

        interval2.shift(dur!"days"(-50));
        assert(interval2 == PosInfInterval!Date(Date(1995, 11, 13)));

  pure nothrow void `expand`(D)(D `duration`)
  if (__traits(compiles, begin + `duration`));
    Expands the interval backwards in time. Effectively, it does begin -= duration.
    Parameters:

    D `duration` | The duration to expand the interval by.

    Example

        auto interval1 = PosInfInterval!Date(Date(1996, 1, 2));
        auto interval2 = PosInfInterval!Date(Date(1996, 1, 2));

        interval1.expand(dur!"days"(2));
        assert(interval1 == PosInfInterval!Date(Date(1995, 12, 31)));

        interval2.expand(dur!"days"(-2));
        assert(interval2 == PosInfInterval!Date(Date(1996, 1, 4)));

  void `expand`(T)(T `years`, T `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (isIntegral!T);
    Expands the interval forwards and/or backwards in time. Effectively, it subtracts the given number of months/years from begin.
    Parameters:

    T `years` | The number of years to expand the interval by.
    T `months` | The number of months to expand the interval by.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on begin, causing its month to increment.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty or if the resulting interval would be invalid.

    Example

        auto interval1 = PosInfInterval!Date(Date(1996, 1, 2));
        auto interval2 = PosInfInterval!Date(Date(1996, 1, 2));

        interval1.expand(2);
        assert(interval1 == PosInfInterval!Date(Date(1994, 1, 2)));

        interval2.expand(-2);
        assert(interval2 == PosInfInterval!Date(Date(1998, 1, 2)));

  const PosInfIntervalRange!TP `fwdRange`(TP delegate(scope const TP) `func`, PopFirst `popFirst` = PopFirst.no);
    Returns a range which iterates forward over the interval, starting at begin, using func to generate each successive time point.
    The range's front is the interval's begin. func is used to generate the next front when popFront is called. If popFirst is PopFirst.yes, then popFront is called before the range is returned (so that front is a time point which func would generate).
    If func ever generates a time point less than or equal to the current front of the range, then a std.datetime.date.DateTimeException will be thrown.
    There are helper functions in this module which generate common delegates to pass to `fwdRange`. Their documentation starts with "Range-generating function," to make them easily searchable.
    Parameters:

    TP delegate(scope const TP) `func` | The function used to generate the time points of the range over the interval.
    PopFirst `popFirst` | Whether popFront should be called on the range before returning it.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Warning func must be logically pure. Ideally, func would be a function pointer to a pure function, but forcing func to be pure is far too restrictive to be useful, and in order to have the ease of use of having functions which generate functions to pass to `fwdRange`, func must be a delegate.

    If func retains state which changes as it is called, then some algorithms will not work correctly, because the range's save will have failed to have really saved the range's state. To avoid such bugs, don't pass a delegate which is not logically pure to `fwdRange`. If func is given the same time point with two different calls, it must return the same result both times.
    Of course, none of the functions in this module have this problem, so it's only relevant for custom delegates.

    Example

        auto interval = PosInfInterval!Date(Date(2010, 9, 1));
        auto func = delegate (scope const Date date) //For iterating over even-numbered days.
                    {
                        if ((date.day & 1) == 0)
                            return date + dur!"days"(2);

                        return date + dur!"days"(1);
                    };
        auto range = interval.fwdRange(func);

        //An odd day. Using PopFirst.yes would have made this Date(2010, 9, 2).
        assert(range.front == Date(2010, 9, 1));

        range.popFront();
        assert(range.front == Date(2010, 9, 2));

        range.popFront();
        assert(range.front == Date(2010, 9, 4));

        range.popFront();
        assert(range.front == Date(2010, 9, 6));

        range.popFront();
        assert(range.front == Date(2010, 9, 8));

        range.popFront();
        assert(!range.empty);

  const nothrow string `toString`();
    Converts this interval to a string.
struct `NegInfInterval`(TP);
  Represents an interval of time which has negative infinity as its starting point.
  Any ranges which iterate over a `NegInfInterval` are infinite. So, the main purpose of using `NegInfInterval` is to create an infinite range which starts at negative infinity and goes to a fixed end point. Iterate over it in reverse.
  pure nothrow this(scope const TP `end`);
    Parameters:

    TP `end` | The time point which ends the interval.

    Example

        auto interval = PosInfInterval!Date(Date(1996, 1, 2));

  pure nothrow ref NegInfInterval `opAssign`(const ref NegInfInterval `rhs`);
    Parameters:

    NegInfInterval `rhs` | The NegInfInterval to assign to this one.

  pure nothrow ref NegInfInterval `opAssign`(NegInfInterval `rhs`);
    Parameters:

    NegInfInterval `rhs` | The NegInfInterval to assign to this one.

  const pure nothrow @property TP `end`();
    The end point of the interval. It is excluded from the interval.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).end == Date(2012, 3, 1));

  pure nothrow @property void `end`(TP `timePoint`);
    The end point of the interval. It is excluded from the interval.
    Parameters:

    TP `timePoint` | The time point to set end to.

  enum bool `empty`;
    Whether the interval's length is 0. Always returns false.

    Example

        assert(!NegInfInterval!Date(Date(1996, 1, 2)).empty);

  const pure nothrow bool `contains`(TP `timePoint`);
    Whether the given time point is within this interval.
    Parameters:

    TP `timePoint` | The time point to check for inclusion in this interval.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).contains(Date(1994, 12, 24)));
        assert(NegInfInterval!Date(Date(2012, 3, 1)).contains(Date(2000, 1, 5)));
        assert(!NegInfInterval!Date(Date(2012, 3, 1)).contains(Date(2012, 3, 1)));

  const pure bool `contains`(scope const Interval!TP `interval`);
    Whether the given interval is completely within this interval.
    Parameters:

    Interval!TP `interval` | The interval to check for inclusion in this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).contains(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).contains(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).contains(
                    Interval!Date(Date(1998, 2, 28), Date(2013, 5, 1))));

  const pure nothrow bool `contains`(scope const PosInfInterval!TP `interval`);
    Whether the given interval is completely within this interval.
    Always returns false because an interval beginning at negative infinity can never contain an interval going to positive infinity.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check for inclusion in this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).contains(
                    PosInfInterval!Date(Date(1999, 5, 4))));

  const pure nothrow bool `contains`(scope const NegInfInterval `interval`);
    Whether the given interval is completely within this interval.
    Parameters:

    NegInfInterval `interval` | The interval to check for inclusion in this interval.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).contains(
                    NegInfInterval!Date(Date(1996, 5, 4))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).contains(
                    NegInfInterval!Date(Date(2013, 7, 9))));

  const pure nothrow bool `isBefore`(scope const TP `timePoint`);
    Whether this interval is before the given time point.
    Parameters:

    TP `timePoint` | The time point to check whether this interval is before it.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(Date(1994, 12, 24)));
        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(Date(2000, 1, 5)));
        assert(NegInfInterval!Date(Date(2012, 3, 1)).isBefore(Date(2012, 3, 1)));

  const pure bool `isBefore`(scope const Interval!TP `interval`);
    Whether this interval is before the given interval and does not intersect it.
    Parameters:

    Interval!TP `interval` | The interval to check for against this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    Interval!Date(Date(2022, 10, 19), Date(2027, 6, 3))));

  const pure nothrow bool `isBefore`(scope const PosInfInterval!TP `interval`);
    Whether this interval is before the given interval and does not intersect it.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check for against this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    PosInfInterval!Date(Date(2012, 3, 1))));

  const pure nothrow bool `isBefore`(scope const NegInfInterval `interval`);
    Whether this interval is before the given interval and does not intersect it.
    Always returns false because an interval beginning at negative infinity can never be before another interval beginning at negative infinity.
    Parameters:

    NegInfInterval `interval` | The interval to check for against this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    NegInfInterval!Date(Date(1996, 5, 4))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isBefore(
                    NegInfInterval!Date(Date(2013, 7, 9))));

  const pure nothrow bool `isAfter`(scope const TP `timePoint`);
    Whether this interval is after the given time point.
    Always returns false because an interval beginning at negative infinity can never be after any time point.
    Parameters:

    TP `timePoint` | The time point to check whether this interval is after it.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(Date(1994, 12, 24)));
        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(Date(2000, 1, 5)));
        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(Date(2012, 3, 1)));

  const pure bool `isAfter`(scope const Interval!TP `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Always returns false (unless the given interval is empty) because an interval beginning at negative infinity can never be after any other interval.
    Parameters:

    Interval!TP `interval` | The interval to check against this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    Interval!Date(Date(2022, 10, 19), Date(2027, 6, 3))));

  const pure nothrow bool `isAfter`(scope const PosInfInterval!TP `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Always returns false because an interval beginning at negative infinity can never be after any other interval.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check against this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    PosInfInterval!Date(Date(2012, 3, 1))));

  const pure nothrow bool `isAfter`(scope const NegInfInterval `interval`);
    Whether this interval is after the given interval and does not intersect it.
    Always returns false because an interval beginning at negative infinity can never be after any other interval.
    Parameters:

    NegInfInterval `interval` | The interval to check against this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    NegInfInterval!Date(Date(1996, 5, 4))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAfter(
                    NegInfInterval!Date(Date(2013, 7, 9))));

  const pure bool `intersects`(scope const Interval!TP `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    Interval!TP `interval` | The interval to check for intersection with this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    Interval!Date(Date(2022, 10, 19), Date(2027, 6, 3))));

  const pure nothrow bool `intersects`(scope const PosInfInterval!TP `interval`);
    Whether the given interval overlaps this interval.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check for intersection with this interval.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    PosInfInterval!Date(Date(2012, 3, 1))));

  const pure nothrow bool `intersects`(scope const NegInfInterval!TP `interval`);
    Whether the given interval overlaps this interval.
    Always returns true because two intervals beginning at negative infinity always overlap.
    Parameters:

    NegInfInterval!TP `interval` | The interval to check for intersection with this interval.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    NegInfInterval!Date(Date(1996, 5, 4))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersects(
                    NegInfInterval!Date(Date(2013, 7, 9))));

  const Interval!TP `intersection`(scope const Interval!TP `interval`);
    Returns the intersection of two intervals
    Parameters:

    Interval!TP `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect or if the given interval is empty.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersection(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               Interval!Date(Date(1990, 7 , 6), Date(2000, 8, 2)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersection(
                    Interval!Date(Date(1999, 1, 12), Date(2015, 9, 2))) ==
               Interval!Date(Date(1999, 1 , 12), Date(2012, 3, 1)));

  const Interval!TP `intersection`(scope const PosInfInterval!TP `interval`);
    Returns the intersection of two intervals
    Parameters:

    PosInfInterval!TP `interval` | The interval to intersect with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersection(
                    PosInfInterval!Date(Date(1990, 7, 6))) ==
               Interval!Date(Date(1990, 7 , 6), Date(2012, 3, 1)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersection(
                    PosInfInterval!Date(Date(1999, 1, 12))) ==
               Interval!Date(Date(1999, 1 , 12), Date(2012, 3, 1)));

  const nothrow NegInfInterval `intersection`(scope const NegInfInterval `interval`);
    Returns the intersection of two intervals
    Parameters:

    NegInfInterval `interval` | The interval to intersect with this interval.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersection(
                    NegInfInterval!Date(Date(1999, 7, 6))) ==
               NegInfInterval!Date(Date(1999, 7 , 6)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).intersection(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

  const pure bool `isAdjacent`(scope const Interval!TP `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    Interval!TP `interval` | The interval to check whether its adjecent to this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(1999, 1, 12), Date(2012, 3, 1))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(2012, 3, 1), Date(2019, 2, 2))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    Interval!Date(Date(2022, 10, 19), Date(2027, 6, 3))));

  const pure nothrow bool `isAdjacent`(scope const PosInfInterval!TP `interval`);
    Whether the given interval is adjacent to this interval.
    Parameters:

    PosInfInterval!TP `interval` | The interval to check whether its adjecent to this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    PosInfInterval!Date(Date(1999, 5, 4))));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    PosInfInterval!Date(Date(2012, 3, 1))));

  const pure nothrow bool `isAdjacent`(scope const NegInfInterval `interval`);
    Whether the given interval is adjacent to this interval.
    Always returns false because two intervals beginning at negative infinity can never be adjacent to one another.
    Parameters:

    NegInfInterval `interval` | The interval to check whether its adjecent to this interval.

    Example

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    NegInfInterval!Date(Date(1996, 5, 4))));

        assert(!NegInfInterval!Date(Date(2012, 3, 1)).isAdjacent(
                    NegInfInterval!Date(Date(2012, 3, 1))));

  const NegInfInterval `merge`(scope const Interval!TP `interval`);
    Returns the union of two intervals
    Parameters:

    Interval!TP `interval` | The interval to merge with this interval.

    Throws:
    std.datetime.date.DateTimeException if the two intervals do not intersect and are not adjacent or if the given interval is empty.

    Note There is no overload for `merge` which takes a PosInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).merge(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).merge(
                    Interval!Date(Date(1999, 1, 12), Date(2015, 9, 2))) ==
               NegInfInterval!Date(Date(2015, 9 , 2)));

  const pure nothrow NegInfInterval `merge`(scope const NegInfInterval `interval`);
    Returns the union of two intervals
    Parameters:

    NegInfInterval `interval` | The interval to merge with this interval.

    Note There is no overload for `merge` which takes a PosInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).merge(
                    NegInfInterval!Date(Date(1999, 7, 6))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).merge(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               NegInfInterval!Date(Date(2013, 1 , 12)));

  const pure NegInfInterval `span`(scope const Interval!TP `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    Interval!TP `interval` | The interval to create a span together with this interval.

    Throws:
    std.datetime.date.DateTimeException if the given interval is empty.

    Note There is no overload for `span` which takes a PosInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).span(
                    Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).span(
                    Interval!Date(Date(1999, 1, 12), Date(2015, 9, 2))) ==
               NegInfInterval!Date(Date(2015, 9 , 2)));

        assert(NegInfInterval!Date(Date(1600, 1, 7)).span(
                    Interval!Date(Date(2012, 3, 11), Date(2017, 7, 1))) ==
               NegInfInterval!Date(Date(2017, 7 , 1)));

  const pure nothrow NegInfInterval `span`(scope const NegInfInterval `interval`);
    Returns an interval that covers from the earliest time point of two intervals up to (but not including) the latest time point of two intervals.
    Parameters:

    NegInfInterval `interval` | The interval to create a span together with this interval.

    Note There is no overload for `span` which takes a PosInfInterval, because an interval going from negative infinity to positive infinity is not possible.

    Example

        assert(NegInfInterval!Date(Date(2012, 3, 1)).span(
                    NegInfInterval!Date(Date(1999, 7, 6))) ==
               NegInfInterval!Date(Date(2012, 3 , 1)));

        assert(NegInfInterval!Date(Date(2012, 3, 1)).span(
                    NegInfInterval!Date(Date(2013, 1, 12))) ==
               NegInfInterval!Date(Date(2013, 1 , 12)));

  pure nothrow void `shift`(D)(D `duration`)
  if (__traits(compiles, end + `duration`));
    Shifts the end of this interval forward or backwards in time by the given duration (a positive duration shifts the interval forward; a negative duration shifts it backward). Effectively, it does end += duration.
    Parameters:

    D `duration` | The duration to shift the interval by.

    Example

        auto interval1 = NegInfInterval!Date(Date(2012, 4, 5));
        auto interval2 = NegInfInterval!Date(Date(2012, 4, 5));

        interval1.shift(dur!"days"(50));
        assert(interval1 == NegInfInterval!Date(Date(2012, 5, 25)));

        interval2.shift(dur!"days"(-50));
        assert(interval2 == NegInfInterval!Date( Date(2012, 2, 15)));

  void `shift`(T)(T `years`, T `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (isIntegral!T);
    Shifts the end of this interval forward or backwards in time by the given number of years and/or months (a positive number of years and months shifts the interval forward; a negative number shifts it backward). It adds the years the given years and months to end. It effectively calls add!"`years`"() and then add!"`months`"() on end with the given number of years and months.
    Parameters:

    T `years` | The number of years to shift the interval by.
    T `months` | The number of months to shift the interval by.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on end, causing its month to increment.

    Throws:
    std.datetime.date.DateTimeException if empty is true or if the resulting interval would be invalid.

    Example

        auto interval1 = NegInfInterval!Date(Date(2012, 3, 1));
        auto interval2 = NegInfInterval!Date(Date(2012, 3, 1));

        interval1.shift(2);
        assert(interval1 == NegInfInterval!Date(Date(2014, 3, 1)));

        interval2.shift(-2);
        assert(interval2 == NegInfInterval!Date(Date(2010, 3, 1)));

  pure nothrow void `expand`(D)(D `duration`)
  if (__traits(compiles, end + `duration`));
    Expands the interval forwards in time. Effectively, it does end += duration.
    Parameters:

    D `duration` | The duration to expand the interval by.

    Example

        auto interval1 = NegInfInterval!Date(Date(2012, 3, 1));
        auto interval2 = NegInfInterval!Date(Date(2012, 3, 1));

        interval1.expand(dur!"days"(2));
        assert(interval1 == NegInfInterval!Date(Date(2012, 3, 3)));

        interval2.expand(dur!"days"(-2));
        assert(interval2 == NegInfInterval!Date(Date(2012, 2, 28)));

  void `expand`(T)(T `years`, T `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes)
  if (isIntegral!T);
    Expands the interval forwards and/or backwards in time. Effectively, it adds the given number of months/years to end.
    Parameters:

    T `years` | The number of years to expand the interval by.
    T `months` | The number of months to expand the interval by.
    AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on end, causing their month to increment.

    Throws:
    std.datetime.date.DateTimeException if empty is true or if the resulting interval would be invalid.

    Example

        auto interval1 = NegInfInterval!Date(Date(2012, 3, 1));
        auto interval2 = NegInfInterval!Date(Date(2012, 3, 1));

        interval1.expand(2);
        assert(interval1 == NegInfInterval!Date(Date(2014, 3, 1)));

        interval2.expand(-2);
        assert(interval2 == NegInfInterval!Date(Date(2010, 3, 1)));

  const NegInfIntervalRange!TP `bwdRange`(TP delegate(scope const TP) `func`, PopFirst `popFirst` = PopFirst.no);
    Returns a range which iterates backwards over the interval, starting at end, using func to generate each successive time point.
    The range's front is the interval's end. func is used to generate the next front when popFront is called. If popFirst is PopFirst.yes, then popFront is called before the range is returned (so that front is a time point which func would generate).
    If func ever generates a time point greater than or equal to the current front of the range, then a std.datetime.date.DateTimeException will be thrown.
    There are helper functions in this module which generate common delegates to pass to `bwdRange`. Their documentation starts with "Range-generating function," to make them easily searchable.
    Parameters:

    TP delegate(scope const TP) `func` | The function used to generate the time points of the range over the interval.
    PopFirst `popFirst` | Whether popFront should be called on the range before returning it.

    Throws:
    std.datetime.date.DateTimeException if this interval is empty.

    Warning func must be logically pure. Ideally, func would be a function pointer to a pure function, but forcing func to be pure is far too restrictive to be useful, and in order to have the ease of use of having functions which generate functions to pass to fwdRange, func must be a delegate.

    If func retains state which changes as it is called, then some algorithms will not work correctly, because the range's save will have failed to have really saved the range's state. To avoid such bugs, don't pass a delegate which is not logically pure to fwdRange. If func is given the same time point with two different calls, it must return the same result both times.
    Of course, none of the functions in this module have this problem, so it's only relevant for custom delegates.

    Example

        auto interval = NegInfInterval!Date(Date(2010, 9, 9));
        auto func = delegate (scope const Date date) //For iterating over even-numbered days.
                    {
                        if ((date.day & 1) == 0)
                            return date - dur!"days"(2);

                        return date - dur!"days"(1);
                    };
        auto range = interval.bwdRange(func);

        assert(range.front == Date(2010, 9, 9)); //An odd day. Using PopFirst.yes would have made this Date(2010, 9, 8).

        range.popFront();
        assert(range.front == Date(2010, 9, 8));

        range.popFront();
        assert(range.front == Date(2010, 9, 6));

        range.popFront();
        assert(range.front == Date(2010, 9, 4));

        range.popFront();
        assert(range.front == Date(2010, 9, 2));

        range.popFront();
        assert(!range.empty);

  const nothrow string `toString`();
    Converts this interval to a string.
nothrow TP delegate(scope const TP) `everyDayOfWeek`(TP, Direction dir = Direction.fwd)(DayOfWeek `dayOfWeek`)
if (isTimePoint!TP && (dir == Direction.fwd || dir == Direction.bwd) && __traits(hasMember, TP, "`dayOfWeek`") && !__traits(isStaticFunction, TP.`dayOfWeek`) && is(typeof(TP.`dayOfWeek`) == DayOfWeek));
  Range-generating function.
  Returns a delegate which returns the next time point with the given DayOfWeek in a range.
  Using this delegate allows iteration over successive time points which are all the same day of the week. e.g. passing DayOfWeek.mon to `everyDayOfWeek` would result in a delegate which could be used to iterate over all of the Mondays in a range.
  Parameters:

  dir | The direction to iterate in. If passing the return value to fwdRange, use Direction.fwd. If passing it to bwdRange, use Direction.bwd.
  DayOfWeek `dayOfWeek` | The week that each time point in the range will be.

  Examples:

      import std.datetime.date : Date, DayOfWeek;

      auto interval = Interval!Date(Date(2010, 9, 2), Date(2010, 9, 27));
      auto func = everyDayOfWeek!Date(DayOfWeek.mon);
      auto range = interval.fwdRange(func);

      // A Thursday. Using PopFirst.yes would have made this Date(2010, 9, 6).
      writeln(range.front); // Date(2010, 9, 2)

      range.popFront();
      writeln(range.front); // Date(2010, 9, 6)

      range.popFront();
      writeln(range.front); // Date(2010, 9, 13)

      range.popFront();
      writeln(range.front); // Date(2010, 9, 20)

      range.popFront();
      assert(range.empty);

TP delegate(scope const TP) `everyMonth`(TP, Direction dir = Direction.fwd)(int `month`)
if (isTimePoint!TP && (dir == Direction.fwd || dir == Direction.bwd) && __traits(hasMember, TP, "`month`") && !__traits(isStaticFunction, TP.`month`) && is(typeof(TP.`month`) == Month));
  Range-generating function.
  Returns a delegate which returns the next time point with the given month which would be reached by adding months to the given time point.
  So, using this delegate allows iteration over successive time points which are in the same month but different years. For example, iterate over each successive December 25th in an interval by starting with a date which had the 25th as its day and passed Month.dec to `everyMonth` to create the delegate.
  Since it wouldn't really make sense to be iterating over a specific month and end up with some of the time points in the succeeding month or two years after the previous time point, AllowDayOverflow.no is always used when calculating the next time point.
  Parameters:

  dir | The direction to iterate in. If passing the return value to fwdRange, use Direction.fwd. If passing it to bwdRange, use Direction.bwd.
  int `month` | The month that each time point in the range will be in (January is 1).

  Examples:

      import std.datetime.date : Date, Month;

      auto interval = Interval!Date(Date(2000, 1, 30), Date(2004, 8, 5));
      auto func = everyMonth!Date(Month.feb);
      auto range = interval.fwdRange(func);

      // Using PopFirst.yes would have made this Date(2010, 2, 29).
      writeln(range.front); // Date(2000, 1, 30)

      range.popFront();
      writeln(range.front); // Date(2000, 2, 29)

      range.popFront();
      writeln(range.front); // Date(2001, 2, 28)

      range.popFront();
      writeln(range.front); // Date(2002, 2, 28)

      range.popFront();
      writeln(range.front); // Date(2003, 2, 28)

      range.popFront();
      writeln(range.front); // Date(2004, 2, 28)

      range.popFront();
      assert(range.empty);

nothrow TP delegate(scope const TP) `everyDuration`(TP, Direction dir = Direction.fwd, D)(D `duration`)
if (isTimePoint!TP && __traits(compiles, TP.init + `duration`) && (dir == Direction.fwd || dir == Direction.bwd));
  Range-generating function.
  Returns a delegate which returns the next time point which is the given duration later.
  Using this delegate allows iteration over successive time points which are apart by the given duration e.g. passing dur!"days"(3) to `everyDuration` would result in a delegate which could be used to iterate over a range of days which are each 3 days apart.
  Parameters:

  dir | The direction to iterate in. If passing the return value to fwdRange, use Direction.fwd. If passing it to bwdRange, use Direction.bwd.
  D `duration` | The duration which separates each successive time point in the range.

  Examples:

      import core.time : dur;
      import std.datetime.date : Date;

      auto interval = Interval!Date(Date(2010, 9, 2), Date(2010, 9, 27));
      auto func = everyDuration!Date(dur!"days"(8));
      auto range = interval.fwdRange(func);

      // Using PopFirst.yes would have made this Date(2010, 9, 10).
      writeln(range.front); // Date(2010, 9, 2)

      range.popFront();
      writeln(range.front); // Date(2010, 9, 10)

      range.popFront();
      writeln(range.front); // Date(2010, 9, 18)

      range.popFront();
      writeln(range.front); // Date(2010, 9, 26)

      range.popFront();
      assert(range.empty);

nothrow TP delegate(scope const TP) `everyDuration`(TP, Direction dir = Direction.fwd, D)(int `years`, int `months` = 0, AllowDayOverflow `allowOverflow` = AllowDayOverflow.yes, D `duration` = dur!"days"(0))
if (isTimePoint!TP && __traits(compiles, TP.init + `duration`) && __traits(compiles, TP.init.add!"`years`"(`years`)) && __traits(compiles, TP.init.add!"`months`"(`months`)) && (dir == Direction.fwd || dir == Direction.bwd));
  Range-generating function.
  Returns a delegate which returns the next time point which is the given number of years, month, and duration later.
  The difference between this version of `everyDuration` and the version which just takes a core.time.Duration is that this one also takes the number of years and months (along with an AllowDayOverflow to indicate whether adding years and months should allow the days to overflow).
  Note that if iterating forward, add!"`years`"() is called on the given time point, then add!"`months`"(), and finally the duration is added to it. However, if iterating backwards, the duration is added first, then add!"`months`"() is called, and finally add!"`years`"() is called. That way, going backwards generates close to the same time points that iterating forward does, but since adding years and months is not entirely reversible (due to possible day overflow, regardless of whether AllowDayOverflow.yes or AllowDayOverflow.no is used), it can't be guaranteed that iterating backwards will give the same time points as iterating forward would have (even assuming that the end of the range is a time point which would be returned by the delegate when iterating forward from begin).
  Parameters:

  dir | The direction to iterate in. If passing the return value to fwdRange, use Direction.fwd. If passing it to bwdRange, use Direction.bwd.
  int `years` | The number of years to add to the time point passed to the delegate.
  int `months` | The number of months to add to the time point passed to the delegate.
  AllowDayOverflow `allowOverflow` | Whether the days should be allowed to overflow on begin and end, causing their month to increment.
  D `duration` | The duration to add to the time point passed to the delegate.

  Examples:

      import core.time : dur;
      import std.datetime.date : AllowDayOverflow, Date;

      auto interval = Interval!Date(Date(2010, 9, 2), Date(2025, 9, 27));
      auto func = everyDuration!Date(4, 1, AllowDayOverflow.yes, dur!"days"(2));
      auto range = interval.fwdRange(func);

      // Using PopFirst.yes would have made this Date(2014, 10, 12).
      writeln(range.front); // Date(2010, 9, 2)

      range.popFront();
      writeln(range.front); // Date(2014, 10, 4)

      range.popFront();
      writeln(range.front); // Date(2018, 11, 6)

      range.popFront();
      writeln(range.front); // Date(2022, 12, 8)

      range.popFront();
      assert(range.empty);

struct `IntervalRange`(TP, Direction dir) if (isTimePoint!TP && (dir != Direction.both));
  A range over an Interval.
  `IntervalRange` is only ever constructed by Interval. However, when it is constructed, it is given a function, func, which is used to generate the time points which are iterated over. func takes a time point and returns a time point of the same type. For instance, to iterate over all of the days in the interval Interval!Date, pass a function to Interval's fwdRange where that function took a std.datetime.date.Date and returned a std.datetime.date.Date which was one day later. That function would then be used by `IntervalRange`'s popFront to iterate over the std.datetime.date.Dates in the interval.
  If dir == Direction.fwd, then a range iterates forward in time, whereas if dir == Direction.bwd, then it iterates backwards in time. So, if dir == Direction.fwd then front == interval.begin, whereas if dir == Direction.bwd then front == interval.end. func must generate a time point going in the proper direction of iteration, or a std.datetime.date.DateTimeException will be thrown. So, to iterate forward in time, the time point that func generates must be later in time than the one passed to it. If it's either identical or earlier in time, then a std.datetime.date.DateTimeException will be thrown. To iterate backwards, then the generated time point must be before the time point which was passed in.
  If the generated time point is ever passed the edge of the range in the proper direction, then the edge of that range will be used instead. So, if iterating forward, and the generated time point is past the interval's end, then front becomes end. If iterating backwards, and the generated time point is before begin, then front becomes begin. In either case, the range would then be empty.
  Also note that while normally the begin of an interval is included in it and its end is excluded from it, if dir == Direction.bwd, then begin is treated as excluded and end is treated as included. This allows for the same behavior in both directions. This works because none of Interval's functions which care about whether begin or end is included or excluded are ever called by `IntervalRange`. interval returns a normal interval, regardless of whether dir == Direction.fwd or if dir == Direction.bwd, so any Interval functions which are called on it which care about whether begin or end are included or excluded will treat begin as included and end as excluded.
  pure nothrow ref IntervalRange `opAssign`(ref IntervalRange `rhs`);
  pure nothrow ref IntervalRange `opAssign`(IntervalRange `rhs`);
    Parameters:

    IntervalRange `rhs` | The IntervalRange to assign to this one.

  const pure nothrow @property bool `empty`();
    Whether this IntervalRange is empty.
  const pure @property TP `front`();
    The first time point in the range.
    Throws:
    std.datetime.date.DateTimeException if the range is empty.
  void `popFront`();
    Pops front from the range, using func to generate the next time point in the range. If the generated time point is beyond the edge of the range, then front is set to that edge, and the range is then empty. So, if iterating forwards, and the generated time point is greater than the interval's end, then front is set to end. If iterating backwards, and the generated time point is less than the interval's begin, then front is set to begin.
    Throws:
    std.datetime.date.DateTimeException if the range is empty or if the generated time point is in the wrong direction (i.e. if iterating forward and the generated time point is before front, or if iterating backwards and the generated time point is after front).
  pure nothrow @property IntervalRange `save`();
    Returns a copy of this.
  const pure nothrow @property Interval!TP `interval`();
    The interval that this IntervalRange currently covers.
  pure nothrow @property TP delegate(scope const TP) `func`();
    The function used to generate the next time point in the range.
  const pure nothrow @property Direction `direction`();
    The Direction that this range iterates in.
struct `PosInfIntervalRange`(TP) if (isTimePoint!TP);
  A range over a PosInfInterval. It is an infinite range.
  `PosInfIntervalRange` is only ever constructed by PosInfInterval. However, when it is constructed, it is given a function, func, which is used to generate the time points which are iterated over. func takes a time point and returns a time point of the same type. For instance, to iterate over all of the days in the interval PosInfInterval!Date, pass a function to PosInfInterval's fwdRange where that function took a std.datetime.date.Date and returned a std.datetime.date.Date which was one day later. That function would then be used by `PosInfIntervalRange`'s popFront to iterate over the std.datetime.date.Dates in the interval - though obviously, since the range is infinite, use a function such as std.range.take with it rather than iterating over all of the dates.
  As the interval goes to positive infinity, the range is always iterated over forwards, never backwards. func must generate a time point going in the proper direction of iteration, or a std.datetime.date.DateTimeException will be thrown. So, the time points that func generates must be later in time than the one passed to it. If it's either identical or earlier in time, then a std.datetime.date.DateTimeException will be thrown.
  pure nothrow ref PosInfIntervalRange `opAssign`(ref PosInfIntervalRange `rhs`);
  pure nothrow ref PosInfIntervalRange `opAssign`(PosInfIntervalRange `rhs`);
    Parameters:

    PosInfIntervalRange `rhs` | The PosInfIntervalRange to assign to this one.

  enum bool `empty`;
    This is an infinite range, so it is never empty.
  const pure nothrow @property TP `front`();
    The first time point in the range.
  void `popFront`();
    Pops front from the range, using func to generate the next time point in the range.
    Throws:
    std.datetime.date.DateTimeException if the generated time point is less than front.
  pure nothrow @property PosInfIntervalRange `save`();
    Returns a copy of this.
  const pure nothrow @property PosInfInterval!TP `interval`();
    The interval that this range currently covers.
  pure nothrow @property TP delegate(scope const TP) `func`();
    The function used to generate the next time point in the range.
struct `NegInfIntervalRange`(TP) if (isTimePoint!TP);
  A range over a NegInfInterval. It is an infinite range.
  `NegInfIntervalRange` is only ever constructed by NegInfInterval. However, when it is constructed, it is given a function, func, which is used to generate the time points which are iterated over. func takes a time point and returns a time point of the same type. For instance, to iterate over all of the days in the interval NegInfInterval!Date, pass a function to NegInfInterval's bwdRange where that function took a std.datetime.date.Date and returned a std.datetime.date.Date which was one day earlier. That function would then be used by `NegInfIntervalRange`'s popFront to iterate over the std.datetime.date.Dates in the interval - though obviously, since the range is infinite, use a function such as std.range.take with it rather than iterating over all of the dates.
  As the interval goes to negative infinity, the range is always iterated over backwards, never forwards. func must generate a time point going in the proper direction of iteration, or a std.datetime.date.DateTimeException will be thrown. So, the time points that func generates must be earlier in time than the one passed to it. If it's either identical or later in time, then a std.datetime.date.DateTimeException will be thrown.
  Also note that while normally the end of an interval is excluded from it, `NegInfIntervalRange` treats it as if it were included. This allows for the same behavior as with PosInfIntervalRange. This works because none of NegInfInterval's functions which care about whether end is included or excluded are ever called by `NegInfIntervalRange`. interval returns a normal interval, so any NegInfInterval functions which are called on it which care about whether end is included or excluded will treat end as excluded.
  pure nothrow ref NegInfIntervalRange `opAssign`(ref NegInfIntervalRange `rhs`);
  pure nothrow ref NegInfIntervalRange `opAssign`(NegInfIntervalRange `rhs`);
    Parameters:

    NegInfIntervalRange `rhs` | The NegInfIntervalRange to assign to this one.

  enum bool `empty`;
    This is an infinite range, so it is never empty.
  const pure nothrow @property TP `front`();
    The first time point in the range.
  void `popFront`();
    Pops front from the range, using func to generate the next time point in the range.
    Throws:
    std.datetime.date.DateTimeException if the generated time point is greater than front.
  pure nothrow @property NegInfIntervalRange `save`();
    Returns a copy of this.
  const pure nothrow @property NegInfInterval!TP `interval`();
    The interval that this range currently covers.
  pure nothrow @property TP delegate(scope const TP) `func`();
    The function used to generate the next time point in the range.

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