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# std.algorithm.searching

This is a submodule of std.algorithm. It contains generic searching algorithms.

Cheat Sheet
Function Name | Description
--- | ---
all | all!"a > 0"([1, 2, 3, 4]) returns true because all elements are positive
any | any!"a > 0"([1, 2, -3, -4]) returns true because at least one element is positive
balancedParens | balancedParens("((1 + 1) / 2)") returns true because the string has balanced parentheses.
boyerMooreFinder | find("hello world", boyerMooreFinder("or")) returns "orld" using the Boyer-Moore algorithm.
canFind | canFind("hello world", "or") returns true.
count | Counts elements that are equal to a specified value or satisfy a predicate. count([1, 2, 1], 1) returns 2 and count!"a < 0"([1, -3, 0]) returns 1.
countUntil | countUntil(a, b) returns the number of steps taken in a to reach b; for example, countUntil("hello!", "o") returns 4.
commonPrefix | commonPrefix("parakeet", "parachute") returns "para".
endsWith | endsWith("rocks", "ks") returns true.
find | find("hello world", "or") returns "orld" using linear search. (For binary search refer to std.range.SortedRange.)
findAdjacent | findAdjacent([1, 2, 3, 3, 4]) returns the subrange starting with two equal adjacent elements, i.e. [3, 3, 4].
findAmong | findAmong("abcd", "qcx") returns "cd" because 'c' is among "qcx".
findSkip | If a = "abcde", then findSkip(a, "x") returns false and leaves a unchanged, whereas findSkip(a, "c") advances a to "de" and returns true.
findSplit | findSplit("abcdefg", "de") returns a tuple of three ranges "abc", "de", and "fg".
findSplitAfter | findSplitAfter("abcdefg", "de") returns a tuple of two ranges "abcde" and "fg".
findSplitBefore | findSplitBefore("abcdefg", "de") returns a tuple of two ranges "abc" and "defg".
minCount | minCount([2, 1, 1, 4, 1]) returns tuple(1, 3).
maxCount | maxCount([2, 4, 1, 4, 1]) returns tuple(4, 2).
minElement | Selects the minimal element of a range. minElement([3, 4, 1, 2]) returns 1.
maxElement | Selects the maximal element of a range. maxElement([3, 4, 1, 2]) returns 4.
minIndex | Index of the minimal element of a range. minIndex([3, 4, 1, 2]) returns 2.
maxIndex | Index of the maximal element of a range. maxIndex([3, 4, 1, 2]) returns 1.
minPos | minPos([2, 3, 1, 3, 4, 1]) returns the subrange [1, 3, 4, 1], i.e., positions the range at the first occurrence of its minimal element.
maxPos | maxPos([2, 3, 1, 3, 4, 1]) returns the subrange [4, 1], i.e., positions the range at the first occurrence of its maximal element.
skipOver | Assume a = "blah". Then skipOver(a, "bi") leaves a unchanged and returns false, whereas skipOver(a, "bl") advances a to refer to "ah" and returns true.
startsWith | startsWith("hello, world", "hello") returns true.
until | Lazily iterates a range until a specific value is found.

License:
Boost License 1.0.
Authors:
Andrei Alexandrescu

Source std/algorithm/searching.d

template `all`(alias pred = "a")
  Checks if all of the elements satisfy pred.
  Examples:

      assert( all!"a & 1"([1, 3, 5, 7, 9]));
      assert(!all!"a & 1"([1, 2, 3, 5, 7, 9]));

  Examples:
  `all` can also be used without a predicate, if its items can be evaluated to true or false in a conditional statement. This can be a convenient way to quickly evaluate that all of the elements of a range are true.

      int[3] vals = [5, 3, 18];
      assert( all(vals[]));

  bool `all`(Range)(Range `range`)
  if (isInputRange!Range);
    Returns true if and only if the input range `range` is empty or all values found in `range` satisfy the predicate pred. Performs (at most) Ο(range.length) evaluations of pred.
template `any`(alias pred = "a")
  Checks if any of the elements satisfies pred. !`any` can be used to verify that none of the elements satisfy pred. This is sometimes called exists in other languages.
  Examples:

      import std.ascii : isWhite;
      assert( all!(any!isWhite)(["a a", "b b"]));
      assert(!any!(all!isWhite)(["a a", "b b"]));

  Examples:
  `any` can also be used without a predicate, if its items can be evaluated to true or false in a conditional statement. !`any` can be a convenient way to quickly test that none of the elements of a range evaluate to true.

      int[3] vals1 = [0, 0, 0];
      assert(!any(vals1[])); //none of vals1 evaluate to true

      int[3] vals2 = [2, 0, 2];
      assert( any(vals2[]));
      assert(!all(vals2[]));

      int[3] vals3 = [3, 3, 3];
      assert( any(vals3[]));
      assert( all(vals3[]));

  bool `any`(Range)(Range `range`)
  if (isInputRange!Range && is(typeof(unaryFun!pred(`range`.front))));
    Returns true if and only if the input range `range` is non-empty and any value found in `range` satisfies the predicate pred. Performs (at most) Ο(range.length) evaluations of pred.
bool `balancedParens`(Range, E)(Range `r`, E `lPar`, E `rPar`, size_t `maxNestingLevel` = size_t.max)
if (isInputRange!Range && is(typeof(`r`.front == `lPar`)));
  Checks whether `r` has "balanced parentheses", i.e. all instances of `lPar` are closed by corresponding instances of `rPar`. The parameter `maxNestingLevel` controls the nesting level allowed. The most common uses are the default or 0. In the latter case, no nesting is allowed.
  Parameters:

  Range `r` | The range to check.
  E `lPar` | The element corresponding with a left (opening) parenthesis.
  E `rPar` | The element corresponding with a right (closing) parenthesis.
  size_t `maxNestingLevel` | The maximum allowed nesting level.

  Returns:
  true if the given range has balanced parenthesis within the given maximum nesting level; false otherwise.
  Examples:

      auto s = "1 + (2 * (3 + 1 / 2)";
      assert(!balancedParens(s, '(', ')'));
      s = "1 + (2 * (3 + 1) / 2)";
      assert(balancedParens(s, '(', ')'));
      s = "1 + (2 * (3 + 1) / 2)";
      assert(!balancedParens(s, '(', ')', 0));
      s = "1 + (2 * 3 + 1) / (2 - 5)";
      assert(balancedParens(s, '(', ')', 0));
      s = "f(x) = ⌈x⌉";
      assert(balancedParens(s, '⌈', '⌉'));

struct `BoyerMooreFinder`(alias pred, Range);
BoyerMooreFinder!(binaryFun!pred, Range) `boyerMooreFinder`(alias pred = "a == b", Range)(Range `needle`)
if (isRandomAccessRange!Range && hasSlicing!Range || isSomeString!Range);
  Sets up Boyer-Moore matching for use with find below. By default, elements are compared for equality.
  `BoyerMooreFinder` allocates GC memory.
  Parameters:

  pred | Predicate used to compare elements.
  Range `needle` | A random-access range with length and slicing.

  Returns:
  An instance of `BoyerMooreFinder` that can be used with find() to invoke the Boyer-Moore matching algorithm for finding of `needle` in a given haystack.
  Examples:

      auto bmFinder = boyerMooreFinder("TG");

      string r = "TAGTGCCTGA";
      // search for the first match in the haystack r
      r = bmFinder.beFound(r);
      writeln(r); // "TGCCTGA"

      // continue search in haystack
      r = bmFinder.beFound(r[2 .. $]);
      writeln(r); // "TGA"

  this(Range `needle`);
  scope Range `beFound`(Range `haystack`);
  @property size_t `length`();
  alias `opDollar` = length;
auto `commonPrefix`(alias pred = "a == b", R1, R2)(R1 `r1`, R2 `r2`)
if (isForwardRange!R1 && isInputRange!R2 && !isNarrowString!R1 && is(typeof(binaryFun!pred(`r1`.front, `r2`.front))));
auto `commonPrefix`(alias pred, R1, R2)(R1 `r1`, R2 `r2`)
if (isNarrowString!R1 && isInputRange!R2 && is(typeof(binaryFun!pred(`r1`.front, `r2`.front))));
auto `commonPrefix`(R1, R2)(R1 `r1`, R2 `r2`)
if (isNarrowString!R1 && isInputRange!R2 && !isNarrowString!R2 && is(typeof(`r1`.front == `r2`.front)));
auto `commonPrefix`(R1, R2)(R1 `r1`, R2 `r2`)
if (isNarrowString!R1 && isNarrowString!R2);
  Returns the common prefix of two ranges.
  Parameters:

  pred | The predicate to use in comparing elements for commonality. Defaults to equality "a == b".
  R1 `r1` | A forward range of elements.
  R2 `r2` | An input range of elements.

  Returns:
  A slice of `r1` which contains the characters that both ranges start with, if the first argument is a string; otherwise, the same as the result of takeExactly(`r1`, n), where n is the number of elements in the common prefix of both ranges.
  See Also:
  std.range.takeExactly
  Examples:

      writeln(commonPrefix("hello, world", "hello, there")); // "hello, "

size_t `count`(alias pred = "a == b", Range, E)(Range `haystack`, E `needle`)
if (isInputRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`haystack`.front, `needle`)) : bool));
size_t `count`(alias pred = "a == b", R1, R2)(R1 `haystack`, R2 `needle`)
if (isForwardRange!R1 && !isInfinite!R1 && isForwardRange!R2 && is(typeof(binaryFun!pred(`haystack`.front, `needle`.front)) : bool));
size_t `count`(alias pred, R)(R `haystack`)
if (isInputRange!R && !isInfinite!R && is(typeof(unaryFun!pred(`haystack`.front)) : bool));
size_t `count`(R)(R `haystack`)
if (isInputRange!R && !isInfinite!R);
  The first version counts the number of elements x in r for which pred(x, value) is true. pred defaults to equality. Performs Ο(haystack.length) evaluations of pred.
  The second version returns the number of times `needle` occurs in `haystack`. Throws an exception if `needle`.empty, as the count of the empty range in any range would be infinite. Overlapped counts are not considered, for example `count`("aaa", "aa") is 1, not 2.
  The third version counts the elements for which pred(x) is true. Performs Ο(haystack.length) evaluations of pred.
  The fourth version counts the number of elements in a range. It is an optimization for the third version: if the given range has the length property the count is returned right away, otherwise performs Ο(haystack.length) to walk the range.

  Note Regardless of the overload, `count` will not accept infinite ranges for `haystack`.

  Parameters:

  pred | The predicate to evaluate.
  Range `haystack` | The range to count.
  E `needle` | The element or sub-range to count in the `haystack`.

  Returns:
  The number of positions in the `haystack` for which pred returned true.
  Examples:

      import std.uni : toLower;

      // count elements in range
      int[] a = [ 1, 2, 4, 3, 2, 5, 3, 2, 4 ];
      writeln(count(a)); // 9
      writeln(count(a, 2)); // 3
      writeln(count!("a > b")(a, 2)); // 5
      // count range in range
      writeln(count("abcadfabf", "ab")); // 2
      writeln(count("ababab", "abab")); // 1
      writeln(count("ababab", "abx")); // 0
      // fuzzy count range in range
      writeln(count!((a, b) => toLower(a) == toLower(b))("AbcAdFaBf", "ab")); // 2
      // count predicate in range
      writeln(count!("a > 1")(a)); // 8

ptrdiff_t `countUntil`(alias pred = "a == b", R, Rs...)(R `haystack`, Rs `needles`)
if (isForwardRange!R && (Rs.length > 0) && (isForwardRange!(Rs[0]) == isInputRange!(Rs[0])) && allSatisfy!(canTestStartsWith!(pred, R), Rs));
ptrdiff_t `countUntil`(alias pred = "a == b", R, N)(R `haystack`, N `needle`)
if (isInputRange!R && is(typeof(binaryFun!pred(`haystack`.front, `needle`)) : bool));
ptrdiff_t `countUntil`(alias pred, R)(R `haystack`)
if (isInputRange!R && is(typeof(unaryFun!pred(`haystack`.front)) : bool));
  Counts elements in the given forward range until the given predicate is true for one of the given `needles`.
  Parameters:

  pred | The predicate for determining when to stop counting.
  R `haystack` | The input range to be counted.
  Rs `needles` | Either a single element, or a forward range of elements, to be evaluated in turn against each element in `haystack` under the given predicate.

  Returns:
  The number of elements which must be popped from the front of `haystack` before reaching an element for which startsWith!pred(`haystack`, `needles`) is true. If startsWith!pred(`haystack`, `needles`) is not true for any element in `haystack`, then -1 is returned. If only pred is provided, pred(`haystack`) is tested for each element.
  See Also:
  std.string.indexOf
  Examples:

      writeln(countUntil("hello world", "world")); // 6
      writeln(countUntil("hello world", 'r')); // 8
      writeln(countUntil("hello world", "programming")); // -1
      writeln(countUntil("日本語", "本語")); // 1
      writeln(countUntil("日本語", '語')); // 2
      writeln(countUntil("日本語", "五")); // -1
      writeln(countUntil("日本語", '五')); // -1
      writeln(countUntil([0, 7, 12, 22, 9], [12, 22])); // 2
      writeln(countUntil([0, 7, 12, 22, 9], 9)); // 4
      writeln(countUntil!"a > b"([0, 7, 12, 22, 9], 20)); // 3

  Examples:

      import std.ascii : isDigit;
      import std.uni : isWhite;

      writeln(countUntil!(isWhite)("hello world")); // 5
      writeln(countUntil!(isDigit)("hello world")); // -1
      writeln(countUntil!"a > 20"([0, 7, 12, 22, 9])); // 3

uint `endsWith`(alias pred = "a == b", Range, Needles...)(Range `doesThisEnd`, Needles `withOneOfThese`)
if (isBidirectionalRange!Range && (Needles.length > 1) && allSatisfy!(canTestStartsWith!(pred, Range), Needles));
bool `endsWith`(alias pred = "a == b", R1, R2)(R1 `doesThisEnd`, R2 `withThis`)
if (isBidirectionalRange!R1 && isBidirectionalRange!R2 && is(typeof(binaryFun!pred(`doesThisEnd`.back, `withThis`.back)) : bool));
bool `endsWith`(alias pred = "a == b", R, E)(R `doesThisEnd`, E `withThis`)
if (isBidirectionalRange!R && is(typeof(binaryFun!pred(`doesThisEnd`.back, `withThis`)) : bool));
bool `endsWith`(alias pred, R)(R `doesThisEnd`)
if (isInputRange!R && ifTestable!(typeof(`doesThisEnd`.front), unaryFun!pred));
  Checks if the given range ends with (one of) the given needle(s). The reciprocal of startsWith.
  Parameters:

  pred | The predicate to use for comparing elements between the range and the needle(s).
  Range `doesThisEnd` | The bidirectional range to check.
  Needles `withOneOfThese` | The needles to check against, which may be single elements, or bidirectional ranges of elements.
  R2 `withThis` | The single element to check.

  Returns:
  0 if the needle(s) do not occur at the end of the given range; otherwise the position of the matching needle, that is, 1 if the range ends with `withOneOfThese`[0], 2 if it ends with `withOneOfThese`[1], and so on.
  In the case when no needle parameters are given, return true iff back of doesThisStart fulfils predicate pred.
  Examples:

      import std.ascii : isAlpha;
      assert("abc".endsWith!(a => a.isAlpha));
      assert("abc".endsWith!isAlpha);

      assert(!"ab1".endsWith!(a => a.isAlpha));

      assert(!"ab1".endsWith!isAlpha);
      assert(!"".endsWith!(a => a.isAlpha));

      import std.algorithm.comparison : among;
      assert("abc".endsWith!(a => a.among('c', 'd') != 0));
      assert(!"abc".endsWith!(a => a.among('a', 'b') != 0));

      assert(endsWith("abc", ""));
      assert(!endsWith("abc", "b"));
      writeln(endsWith("abc", "a", 'c')); // 2
      writeln(endsWith("abc", "c", "a")); // 1
      writeln(endsWith("abc", "c", "c")); // 1
      writeln(endsWith("abc", "bc", "c")); // 2
      writeln(endsWith("abc", "x", "c", "b")); // 2
      writeln(endsWith("abc", "x", "aa", "bc")); // 3
      writeln(endsWith("abc", "x", "aaa", "sab")); // 0
      writeln(endsWith("abc", "x", "aaa", 'c', "sab")); // 3

InputRange `find`(alias pred = "a == b", InputRange, Element)(InputRange `haystack`, scope Element `needle`)
if (isInputRange!InputRange && is(typeof(binaryFun!pred(`haystack`.front, `needle`)) : bool) && !is(typeof(binaryFun!pred(`haystack`.front, `needle`.front)) : bool));
InputRange `find`(alias pred, InputRange)(InputRange `haystack`)
if (isInputRange!InputRange);
R1 `find`(alias pred = "a == b", R1, R2)(R1 `haystack`, scope R2 `needle`)
if (isForwardRange!R1 && isForwardRange!R2 && is(typeof(binaryFun!pred(`haystack`.front, `needle`.front)) : bool));
  Finds an individual element in an input range. Elements of `haystack` are compared with `needle` by using predicate pred with pred(`haystack`.front, `needle`). `find` performs Ο(walkLength(haystack)) evaluations of pred.
  The predicate is passed to std.functional.binaryFun, and can either accept a string, or any callable that can be executed via pred(element, element).
  To find the last occurrence of `needle` in a bidirectional `haystack`, call `find`(retro(`haystack`), `needle`). See std.range.retro.
  If no `needle` is provided, pred(`haystack`.front) will be evaluated on each element of the input range.
  If input is a forward range, `needle` can be a forward range too. In this case startsWith!pred(`haystack`, `needle`) is evaluated on each evaluation.

  Note `find` behaves similar to dropWhile in other languages.

  Complexity `find` performs Ο(walkLength(haystack)) evaluations of pred. There are specializations that improve performance by taking advantage of bidirectional or random access ranges (where possible).

  Parameters:

  pred | The predicate for comparing each element with the needle, defaulting to equality "a == b". The negated predicate "a != b" can be used to search instead for the first element not matching the needle.
  InputRange `haystack` | The input range searched in.
  Element `needle` | The element searched for.

  Returns:
  `haystack` advanced such that the front element is the one searched for; that is, until binaryFun!pred(`haystack`.front, `needle`) is true. If no such position exists, returns an empty `haystack`.
  See Also:
  findAdjacent, findAmong, findSkip, findSplit, startsWith
  Examples:

      import std.range.primitives;

      auto arr = [1, 2, 4, 4, 4, 4, 5, 6, 9];
      writeln(arr.find(4)); // [4, 4, 4, 4, 5, 6, 9]
      writeln(arr.find(1)); // arr
      writeln(arr.find(9)); // [9]
      writeln(arr.find!((a, b) => a > b)(4)); // [5, 6, 9]
      writeln(arr.find!((a, b) => a < b)(4)); // arr
      assert(arr.find(0).empty);
      assert(arr.find(10).empty);
      assert(arr.find(8).empty);

      writeln(find("hello, world", ',')); // ", world"

  Examples:
  Case-insensitive find of a string

      import std.range.primitives;
      import std.uni : toLower;

      string[] s = ["Hello", "world", "!"];
      writeln(s.find!((a, b) => toLower(a) == b)("hello")); // s

  Examples:

      auto arr = [ 1, 2, 3, 4, 1 ];
      writeln(find!("a > 2")(arr)); // [3, 4, 1]

      // with predicate alias
      bool pred(int x) { return x + 1 > 1.5; }
      writeln(find!(pred)(arr)); // arr

  Examples:

      import std.container : SList;
      import std.range.primitives : empty;
      import std.typecons : Tuple;

      assert(find("hello, world", "World").empty);
      writeln(find("hello, world", "wo")); // "world"
      writeln([1, 2, 3, 4].find(SList!int(2, 3)[])); // [2, 3, 4]
      alias C = Tuple!(int, "x", int, "y");
      auto a = [C(1,0), C(2,0), C(3,1), C(4,0)];
      writeln(a.find!"a.x == b"([2, 3])); // [C(2, 0), C(3, 1), C(4, 0)]
      writeln(a[1 .. $].find!"a.x == b"([2, 3])); // [C(2, 0), C(3, 1), C(4, 0)]

Tuple!(Range, size_t) `find`(alias pred = "a == b", Range, Ranges...)(Range `haystack`, Ranges `needles`)
if (Ranges.length > 1 && is(typeof(startsWith!pred(`haystack`, `needles`))));
  Finds two or more `needles` into a `haystack`. The predicate pred is used throughout to compare elements. By default, elements are compared for equality.
  Parameters:

  pred | The predicate to use for comparing elements.
  Range `haystack` | The target of the search. Must be an input range. If any of `needles` is a range with elements comparable to elements in `haystack`, then `haystack` must be a forward range such that the search can backtrack.
  Ranges `needles` | One or more items to search for. Each of `needles` must be either comparable to one element in `haystack`, or be itself a forward range with elements comparable with elements in `haystack`.

  Returns:
  A tuple containing `haystack` positioned to match one of the needles and also the 1-based index of the matching element in needles (0 if none of `needles` matched, 1 if `needles`[0] matched, 2 if `needles`[1] matched...). The first needle to be found will be the one that matches. If multiple needles are found at the same spot in the range, then the shortest one is the one which matches (if multiple needles of the same length are found at the same spot (e.g "a" and 'a'), then the left-most of them in the argument list matches).
  The relationship between `haystack` and `needles` simply means that one can e.g. search for individual ints or arrays of ints in an array of ints. In addition, if elements are individually comparable, searches of heterogeneous types are allowed as well: a double[] can be searched for an int or a short[], and conversely a long can be searched for a float or a double[]. This makes for efficient searches without the need to coerce one side of the comparison into the other's side type.
  The complexity of the search is Ο(haystack.length * max(needles.length)). (For needles that are individual items, length is considered to be 1.) The strategy used in searching several subranges at once maximizes cache usage by moving in `haystack` as few times as possible.
  Examples:

      import std.typecons : tuple;
      int[] a = [ 1, 4, 2, 3 ];
      writeln(find(a, 4)); // [4, 2, 3]
      writeln(find(a, [1, 4])); // [1, 4, 2, 3]
      writeln(find(a, [1, 3], 4)); // tuple([4, 2, 3], 2)
      // Mixed types allowed if comparable
      writeln(find(a, 5, [1.2, 3.5], 2.0)); // tuple([2, 3], 3)

RandomAccessRange `find`(RandomAccessRange, alias pred, InputRange)(RandomAccessRange `haystack`, scope BoyerMooreFinder!(pred, InputRange) `needle`);
  Finds `needle` in `haystack` efficiently using the Boyer-Moore method.
  Parameters:

  RandomAccessRange `haystack` | A random-access range with length and slicing.
  BoyerMooreFinder!(pred, InputRange) `needle` | A BoyerMooreFinder.

  Returns:
  `haystack` advanced such that `needle` is a prefix of it (if no such position exists, returns `haystack` advanced to termination).
  Examples:

      import std.range.primitives : empty;
      int[] a = [ -1, 0, 1, 2, 3, 4, 5 ];
      int[] b = [ 1, 2, 3 ];

      writeln(find(a, boyerMooreFinder(b))); // [1, 2, 3, 4, 5]
      assert(find(b, boyerMooreFinder(a)).empty);

template `canFind`(alias pred = "a == b")
  Convenience function. Like find, but only returns whether or not the search was successful.
  See Also:
  std.algorithm.comparison.among for checking a value against multiple possibilities.
  Examples:

      writeln(canFind([0, 1, 2, 3], 2)); // true
      assert(canFind([0, 1, 2, 3], [1, 2], [2, 3]));
      writeln(canFind([0, 1, 2, 3], [1, 2], [2, 3])); // 1
      assert(canFind([0, 1, 2, 3], [1, 7], [2, 3]));
      writeln(canFind([0, 1, 2, 3], [1, 7], [2, 3])); // 2

      writeln(canFind([0, 1, 2, 3], 4)); // false
      assert(!canFind([0, 1, 2, 3], [1, 3], [2, 4]));
      writeln(canFind([0, 1, 2, 3], [1, 3], [2, 4])); // 0

  Examples:
  Example using a custom predicate. Note that the needle appears as the second argument of the predicate.

      auto words = [
          "apple",
          "beeswax",
          "cardboard"
      ];
      assert(!canFind(words, "bees"));
      assert( canFind!((string a, string b) => a.startsWith(b))(words, "bees"));

  Examples:
  Search for mutliple items in an array of items (search for needles in an array of hay stacks)

      string s1 = "aaa111aaa";
      string s2 = "aaa222aaa";
      string s3 = "aaa333aaa";
      string s4 = "aaa444aaa";
      const hay = [s1, s2, s3, s4];
      assert(hay.canFind!(e => (e.canFind("111", "222"))));

  bool `canFind`(Range)(Range `haystack`)
  if (is(typeof(find!pred(`haystack`))));
    Returns true if and only if any value v found in the input range range satisfies the predicate pred. Performs (at most) Ο(haystack.length) evaluations of pred.
  bool `canFind`(Range, Element)(Range `haystack`, scope Element `needle`)
  if (is(typeof(find!pred(`haystack`, `needle`))));
    Returns true if and only if `needle` can be found in range. Performs Ο(haystack.length) evaluations of pred.
  size_t `canFind`(Range, Ranges...)(Range `haystack`, scope Ranges `needles`)
  if (Ranges.length > 1 && allSatisfy!(isForwardRange, Ranges) && is(typeof(find!pred(`haystack`, `needles`))));
    Returns the 1-based index of the first needle found in `haystack`. If no needle is found, then 0 is returned.
    So, if used directly in the condition of an if statement or loop, the result will be true if one of the needles is found and false if none are found, whereas if the result is used elsewhere, it can either be cast to bool for the same effect or used to get which needle was found first without having to deal with the tuple that LREF find returns for the same operation.
Range `findAdjacent`(alias pred = "a == b", Range)(Range `r`)
if (isForwardRange!Range);
  Advances `r` until it finds the first two adjacent elements a, b that satisfy pred(a, b). Performs Ο(r.length) evaluations of pred.
  Parameters:

  pred | The predicate to satisfy.
  Range `r` | A forward range to search in.

  Returns:
  `r` advanced to the first occurrence of two adjacent elements that satisfy the given predicate. If there are no such two elements, returns `r` advanced until empty.
  See Also:
  STL's adjacent_find
  Examples:

      int[] a = [ 11, 10, 10, 9, 8, 8, 7, 8, 9 ];
      auto r = findAdjacent(a);
      writeln(r); // [10, 10, 9, 8, 8, 7, 8, 9]
      auto p = findAdjacent!("a < b")(a);
      writeln(p); // [7, 8, 9]

InputRange `findAmong`(alias pred = "a == b", InputRange, ForwardRange)(InputRange `seq`, ForwardRange `choices`)
if (isInputRange!InputRange && isForwardRange!ForwardRange);
  Searches the given range for an element that matches one of the given choices.
  Advances `seq` by calling `seq`.popFront until either find!(pred)(`choices`, `seq`.front) is true, or `seq` becomes empty. Performs Ο(seq.length * choices.length) evaluations of pred.
  Parameters:

  pred | The predicate to use for determining a match.
  InputRange `seq` | The input range to search.
  ForwardRange `choices` | A forward range of possible choices.

  Returns:
  `seq` advanced to the first matching element, or until empty if there are no matching elements.
  See Also:
  find, algorithm.comparison.among.std
  Examples:

      int[] a = [ -1, 0, 1, 2, 3, 4, 5 ];
      int[] b = [ 3, 1, 2 ];
      writeln(findAmong(a, b)); // a[2 .. $]

bool `findSkip`(alias pred = "a == b", R1, R2)(ref R1 `haystack`, R2 `needle`)
if (isForwardRange!R1 && isForwardRange!R2 && is(typeof(binaryFun!pred(`haystack`.front, `needle`.front))));
size_t `findSkip`(alias pred, R1)(ref R1 `haystack`)
if (isForwardRange!R1 && ifTestable!(typeof(`haystack`.front), unaryFun!pred));
  Finds `needle` in `haystack` and positions `haystack` right after the first occurrence of `needle`.
  If no needle is provided, the `haystack` is advanced as long as pred evaluates to true. Similarly, the haystack is positioned so as pred evaluates to false for `haystack`.front.
  Parameters:

  R1 `haystack` | The forward range to search in.
  R2 `needle` | The forward range to search for.
  pred | Custom predicate for comparison of haystack and needle

  Returns:
  true if the needle was found, in which case `haystack` is positioned after the end of the first occurrence of `needle`; otherwise false, leaving `haystack` untouched. If no needle is provided, it returns the number of times pred(`haystack`.front) returned true.
  See Also:
  find
  Examples:

      import std.range.primitives : empty;
      // Needle is found; s is replaced by the substring following the first
      // occurrence of the needle.
      string s = "abcdef";
      assert(findSkip(s, "cd") && s == "ef");

      // Needle is not found; s is left untouched.
      s = "abcdef";
      assert(!findSkip(s, "cxd") && s == "abcdef");

      // If the needle occurs at the end of the range, the range is left empty.
      s = "abcdef";
      assert(findSkip(s, "def") && s.empty);

  Examples:

      import std.ascii : isWhite;
      string s = "    abc";
      assert(findSkip!isWhite(s) && s == "abc");
      assert(!findSkip!isWhite(s) && s == "abc");

      s = "  ";
      writeln(findSkip!isWhite(s)); // 2

auto `findSplit`(alias pred = "a == b", R1, R2)(R1 `haystack`, R2 `needle`)
if (isForwardRange!R1 && isForwardRange!R2);
auto `findSplitBefore`(alias pred = "a == b", R1, R2)(R1 `haystack`, R2 `needle`)
if (isForwardRange!R1 && isForwardRange!R2);
auto `findSplitAfter`(alias pred = "a == b", R1, R2)(R1 `haystack`, R2 `needle`)
if (isForwardRange!R1 && isForwardRange!R2);
  These functions find the first occurrence of `needle` in `haystack` and then split `haystack` as follows.
  `findSplit` returns a tuple result containing three ranges. result[0] is the portion of `haystack` before `needle`, result[1] is the portion of `haystack` that matches `needle`, and result[2] is the portion of `haystack` after the match. If `needle` was not found, result[0] comprehends `haystack` entirely and result[1] and result[2] are empty.
  `findSplitBefore` returns a tuple result containing two ranges. result[0] is the portion of `haystack` before `needle`, and result[1] is the balance of `haystack` starting with the match. If `needle` was not found, result[0] comprehends `haystack` entirely and result[1] is empty.
  `findSplitAfter` returns a tuple result containing two ranges. result[0] is the portion of `haystack` up to and including the match, and result[1] is the balance of `haystack` starting after the match. If `needle` was not found, result[0] is empty and result[1] is `haystack`.
  In all cases, the concatenation of the returned ranges spans the entire `haystack`.
  If `haystack` is a random-access range, all three components of the tuple have the same type as `haystack`. Otherwise, `haystack` must be a forward range and the type of result[0] and result[1] is the same as std.range.takeExactly.
  Parameters:

  pred | Predicate to use for comparing needle against haystack.
  R1 `haystack` | The range to search.
  R2 `needle` | What to look for.

  Returns:
  A sub-type of Tuple!() of the split portions of `haystack` (see above for details). This sub-type of Tuple!() has opCast defined for bool. This opCast returns true when the separating `needle` was found and false otherwise.
  See Also:
  find
  Examples:
  Returning a subtype of std.typecons.Tuple enables the following convenient idiom:

      // findSplit returns a triplet
      if (auto split = "dlang-rocks".findSplit("-"))
      {
          writeln(split[0]); // "dlang"
          writeln(split[1]); // "-"
          writeln(split[2]); // "rocks"
      }
      else assert(0);

      // works with const aswell
      if (const split = "dlang-rocks".findSplit("-"))
      {
          writeln(split[0]); // "dlang"
          writeln(split[1]); // "-"
          writeln(split[2]); // "rocks"
      }
      else assert(0);

  Examples:

      import std.range.primitives : empty;

      auto a = "Carl Sagan Memorial Station";
      auto r = findSplit(a, "Velikovsky");
      import std.typecons : isTuple;
      static assert(isTuple!(typeof(r.asTuple)));
      static assert(isTuple!(typeof(r)));
      assert(!r);
      writeln(r[0]); // a
      assert(r[1].empty);
      assert(r[2].empty);
      r = findSplit(a, " ");
      writeln(r[0]); // "Carl"
      writeln(r[1]); // " "
      writeln(r[2]); // "Sagan Memorial Station"
      if (const r1 = findSplitBefore(a, "Sagan"))
      {
          assert(r1);
          writeln(r1[0]); // "Carl "
          writeln(r1[1]); // "Sagan Memorial Station"
      }
      if (const r2 = findSplitAfter(a, "Sagan"))
      {
          assert(r2);
          writeln(r2[0]); // "Carl Sagan"
          writeln(r2[1]); // " Memorial Station"
      }

  Examples:
  Use std.range.only to find single elements:

      import std.range : only;
      writeln([1, 2, 3, 4].findSplitBefore(only(3))[0]); // [1, 2]

Tuple!(ElementType!Range, size_t) `minCount`(alias pred = "a < b", Range)(Range `range`)
if (isInputRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`range`.front, `range`.front))));
Tuple!(ElementType!Range, size_t) `maxCount`(alias pred = "a < b", Range)(Range `range`)
if (isInputRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`range`.front, `range`.front))));
  Computes the minimum (respectively maximum) of `range` along with its number of occurrences. Formally, the minimum is a value x in `range` such that pred(a, x) is false for all values a in `range`. Conversely, the maximum is a value x in `range` such that pred(x, a) is false for all values a in `range` (note the swapped arguments to pred).
  These functions may be used for computing arbitrary extrema by choosing pred appropriately. For corrrect functioning, pred must be a strict partial order, i.e. transitive (if pred(a, b) && pred(b, c) then pred(a, c)) and irreflexive (pred(a, a) is false). The trichotomy property of inequality is not required: these algorithms consider elements a and b equal (for the purpose of counting) if pred puts them in the same equivalence class, i.e. !pred(a, b) && !pred(b, a).
  Parameters:

  pred | The ordering predicate to use to determine the extremum (minimum or maximum).
  Range `range` | The input range to count.

  Returns:
  The minimum, respectively maximum element of a range together with the number it occurs in the range.

  Limitations If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.maxElement for examples on how to cope with NaNs.

  Throws:
  Exception if `range`.empty.
  See Also:
  std.algorithm.comparison.min, minIndex, minElement, minPos
  Examples:

      import std.conv : text;
      import std.typecons : tuple;

      int[] a = [ 2, 3, 4, 1, 2, 4, 1, 1, 2 ];
      // Minimum is 1 and occurs 3 times
      writeln(a.minCount); // tuple(1, 3)
      // Maximum is 4 and occurs 2 times
      writeln(a.maxCount); // tuple(4, 2)

auto `minElement`(alias map = (a) => a, Range)(Range `r`)
if (isInputRange!Range && !isInfinite!Range);
auto `minElement`(alias map = (a) => a, Range, RangeElementType = ElementType!Range)(Range `r`, RangeElementType `seed`)
if (isInputRange!Range && !isInfinite!Range && !is(CommonType!(ElementType!Range, RangeElementType) == void));
  Iterates the passed range and returns the minimal element. A custom mapping function can be passed to map. In other languages this is sometimes called argmin.

  Complexity O(n) Exactly n - 1 comparisons are needed.

  Parameters:

  map | custom accessor for the comparison key
  Range `r` | range from which the minimal element will be selected
  RangeElementType `seed` | custom seed to use as initial element

  Returns:
  The minimal element of the passed-in range.

  Note If at least one of the arguments is NaN, the result is an unspecified value.

  If you want to ignore NaNs, you can use std.algorithm.iteration.filter and std.math.isNaN to remove them, before applying minElement. Add a suitable seed, to avoid error messages if all elements are NaNs:

      <range>.filter!(a=>!a.isNaN).minElement(<seed>);

  If you want to get NaN as a result if a NaN is present in the range, you can use std.algorithm.iteration.fold and std.math.isNaN:

      <range>.fold!((a,b)=>a.isNaN || b.isNaN ? real.nan : a < b ? a : b);

  See Also:
  maxElement, std.algorithm.comparison.min, minCount, minIndex, minPos
  Examples:

      import std.range : enumerate;
      import std.typecons : tuple;

      writeln([2, 7, 1, 3].minElement); // 1

      // allows to get the index of an element too
      writeln([5, 3, 7, 9].enumerate.minElement!"a.value"); // tuple(1, 3)

      // any custom accessor can be passed
      writeln([[0, 4], [1, 2]].minElement!"a[1]"); // [1, 2]

      // can be seeded
      int[] arr;
      writeln(arr.minElement(1)); // 1

auto `maxElement`(alias map = (a) => a, Range)(Range `r`)
if (isInputRange!Range && !isInfinite!Range);
auto `maxElement`(alias map = (a) => a, Range, RangeElementType = ElementType!Range)(Range `r`, RangeElementType `seed`)
if (isInputRange!Range && !isInfinite!Range && !is(CommonType!(ElementType!Range, RangeElementType) == void));
  Iterates the passed range and returns the maximal element. A custom mapping function can be passed to map. In other languages this is sometimes called argmax.

  Complexity O(n) Exactly n - 1 comparisons are needed.

  Parameters:

  map | custom accessor for the comparison key
  Range `r` | range from which the maximum element will be selected
  RangeElementType `seed` | custom seed to use as initial element

  Returns:
  The maximal element of the passed-in range.

  Note If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.minElement for examples on how to cope with NaNs.

  See Also:
  minElement, std.algorithm.comparison.max, maxCount, maxIndex, maxPos
  Examples:

      import std.range : enumerate;
      import std.typecons : tuple;
      writeln([2, 1, 4, 3].maxElement); // 4

      // allows to get the index of an element too
      writeln([2, 1, 4, 3].enumerate.maxElement!"a.value"); // tuple(2, 4)

      // any custom accessor can be passed
      writeln([[0, 4], [1, 2]].maxElement!"a[1]"); // [0, 4]

      // can be seeded
      int[] arr;
      writeln(arr.minElement(1)); // 1

Range `minPos`(alias pred = "a < b", Range)(Range `range`)
if (isForwardRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`range`.front, `range`.front))));
Range `maxPos`(alias pred = "a < b", Range)(Range `range`)
if (isForwardRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`range`.front, `range`.front))));
  Computes a subrange of `range` starting at the first occurrence of `range`'s minimum (respectively maximum) and with the same ending as `range`, or the empty range if `range` itself is empty.
  Formally, the minimum is a value x in `range` such that pred(a, x) is false for all values a in `range`. Conversely, the maximum is a value x in `range` such that pred(x, a) is false for all values a in `range` (note the swapped arguments to pred).
  These functions may be used for computing arbitrary extrema by choosing pred appropriately. For corrrect functioning, pred must be a strict partial order, i.e. transitive (if pred(a, b) && pred(b, c) then pred(a, c)) and irreflexive (pred(a, a) is false).
  Parameters:

  pred | The ordering predicate to use to determine the extremum (minimum or maximum) element.
  Range `range` | The forward range to search.

  Returns:
  The position of the minimum (respectively maximum) element of forward range `range`, i.e. a subrange of `range` starting at the position of its smallest (respectively largest) element and with the same ending as `range`.

  Limitations If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.maxElement for examples on how to cope with NaNs.

  See Also:
  std.algorithm.comparison.max, minCount, minIndex, minElement
  Examples:

      int[] a = [ 2, 3, 4, 1, 2, 4, 1, 1, 2 ];
      // Minimum is 1 and first occurs in position 3
      writeln(a.minPos); // [1, 2, 4, 1, 1, 2]
      // Maximum is 4 and first occurs in position 2
      writeln(a.maxPos); // [4, 1, 2, 4, 1, 1, 2]

ptrdiff_t `minIndex`(alias pred = "a < b", Range)(Range `range`)
if (isInputRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`range`.front, `range`.front))));
  Computes the index of the first occurrence of `range`'s minimum element.
  Parameters:

  pred | The ordering predicate to use to determine the minimum element.
  Range `range` | The input range to search.

  Complexity Ο(range.length) Exactly `range`.length - 1 comparisons are needed.

  Returns:
  The index of the first encounter of the minimum element in `range`. If the `range` is empty, -1 is returned.

  Limitations If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.maxElement for examples on how to cope with NaNs.

  See Also:
  maxIndex, std.algorithm.comparison.min, minCount, minElement, minPos
  Examples:

      int[] a = [2, 3, 4, 1, 2, 4, 1, 1, 2];

      // Minimum is 1 and first occurs in position 3
      writeln(a.minIndex); // 3
      // Get maximum index with minIndex
      writeln(a.minIndex!"a > b"); // 2

      // Range is empty, so return value is -1
      int[] b;
      writeln(b.minIndex); // -1

      // Works with more custom types
      struct Dog { int age; }
      Dog[] dogs = [Dog(10), Dog(5), Dog(15)];
      writeln(dogs.minIndex!"a.age < b.age"); // 1

ptrdiff_t `maxIndex`(alias pred = "a < b", Range)(Range `range`)
if (isInputRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(`range`.front, `range`.front))));
  Computes the index of the first occurrence of `range`'s maximum element.

  Complexity Ο(range) Exactly `range`.length - 1 comparisons are needed.

  Parameters:

  pred | The ordering predicate to use to determine the maximum element.
  Range `range` | The input range to search.

  Returns:
  The index of the first encounter of the maximum in `range`. If the `range` is empty, -1 is returned.

  Limitations If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.maxElement for examples on how to cope with NaNs.

  See Also:
  minIndex, std.algorithm.comparison.max, maxCount, maxElement, maxPos
  Examples:

      // Maximum is 4 and first occurs in position 2
      int[] a = [2, 3, 4, 1, 2, 4, 1, 1, 2];
      writeln(a.maxIndex); // 2

      // Empty range
      int[] b;
      writeln(b.maxIndex); // -1

      // Works with more custom types
      struct Dog { int age; }
      Dog[] dogs = [Dog(10), Dog(15), Dog(5)];
      writeln(dogs.maxIndex!"a.age < b.age"); // 1

template `skipOver`(alias pred = (a, b) => a == b)
  Skip over the initial portion of the first given range (haystack) that matches any of the additionally given ranges (needles) fully, or if no second range is given skip over the elements that fulfill pred. Do nothing if there is no match.
  Parameters:

  pred | The predicate that determines whether elements from each respective range match. Defaults to equality "a == b".

  Examples:

      import std.algorithm.comparison : equal;

      auto s1 = "Hello world";
      assert(!skipOver(s1, "Ha"));
      writeln(s1); // "Hello world"
      assert(skipOver(s1, "Hell") && s1 == "o world", s1);

      string[]  r1 = ["abc", "def", "hij"];
      dstring[] r2 = ["abc"d];
      assert(!skipOver!((a, b) => a.equal(b))(r1, ["def"d]), r1[0]);
      writeln(r1); // ["abc", "def", "hij"]
      assert(skipOver!((a, b) => a.equal(b))(r1, r2));
      writeln(r1); // ["def", "hij"]

  Examples:

      import std.ascii : isWhite;
      import std.range.primitives : empty;

      auto s2 = "\t\tvalue";
      auto s3 = "";
      auto s4 = "\t\t\t";
      assert(s2.skipOver!isWhite && s2 == "value");
      assert(!s3.skipOver!isWhite);
      assert(s4.skipOver!isWhite && s3.empty);

  Examples:
  Variadic skipOver

      auto s = "Hello world";
      assert(!skipOver(s, "hello", "HellO"));
      writeln(s); // "Hello world"

      // the range is skipped over the longest matching needle is skipped
      assert(skipOver(s, "foo", "hell", "Hello "));
      writeln(s); // "world"

  Examples:

      import std.algorithm.comparison : equal;

      auto s1 = "Hello world";
      assert(!skipOver(s1, 'a'));
      writeln(s1); // "Hello world"
      assert(skipOver(s1, 'H') && s1 == "ello world");

      string[] r = ["abc", "def", "hij"];
      dstring e = "abc"d;
      assert(!skipOver!((a, b) => a.equal(b))(r, "def"d));
      writeln(r); // ["abc", "def", "hij"]
      assert(skipOver!((a, b) => a.equal(b))(r, e));
      writeln(r); // ["def", "hij"]

      auto s2 = "";
      assert(!s2.skipOver('a'));

  Examples:
  Partial instantiation

      import std.ascii : isWhite;
      import std.range.primitives : empty;

      alias whitespaceSkiper = skipOver!isWhite;

      auto s2 = "\t\tvalue";
      auto s3 = "";
      auto s4 = "\t\t\t";
      assert(whitespaceSkiper(s2) && s2 == "value");
      assert(!whitespaceSkiper(s2));
      assert(whitespaceSkiper(s4) && s3.empty);

  bool `skipOver`(Haystack, Needles...)(ref Haystack `haystack`, Needles `needles`)
  if (is(typeof(binaryFun!pred(`haystack`.front, `needles`[0].front))) && isForwardRange!Haystack && allSatisfy!(isInputRange, Needles) && !is(CommonType!(staticMap!(ElementType, staticMap!(Unqual, Needles))) == void));
  bool `skipOver`(R)(ref R `r1`)
  if (isForwardRange!R && ifTestable!(typeof(`r1`.front), unaryFun!pred));
  bool `skipOver`(R, Es...)(ref R `r`, Es `es`)
  if (isInputRange!R && is(typeof(binaryFun!pred(`r`.front, `es`[0]))));
    Parameters:

    Haystack `haystack` | The forward range to move forward.
    Needles `needles` | The input ranges representing the prefix of `r1` to skip over.
    Es `es` | The element to match.

    Returns:
    true if the prefix of `haystack` matches any range of `needles` fully or pred evaluates to true, and `haystack` has been advanced to the point past this segment; otherwise false, and `haystack` is left in its original position.

    Note By definition, empty ranges are matched fully and if `needles` contains an empty range, `skipOver` will return true.

uint `startsWith`(alias pred = (a, b) => a == b, Range, Needles...)(Range `doesThisStart`, Needles `withOneOfThese`)
if (isInputRange!Range && (Needles.length > 1) && allSatisfy!(canTestStartsWith!(pred, Range), Needles));
bool `startsWith`(alias pred = "a == b", R1, R2)(R1 `doesThisStart`, R2 `withThis`)
if (isInputRange!R1 && isInputRange!R2 && is(typeof(binaryFun!pred(`doesThisStart`.front, `withThis`.front)) : bool));
bool `startsWith`(alias pred = "a == b", R, E)(R `doesThisStart`, E `withThis`)
if (isInputRange!R && is(typeof(binaryFun!pred(`doesThisStart`.front, `withThis`)) : bool));
bool `startsWith`(alias pred, R)(R `doesThisStart`)
if (isInputRange!R && ifTestable!(typeof(`doesThisStart`.front), unaryFun!pred));
  Checks whether the given input range starts with (one of) the given needle(s) or, if no needles are given, if its front element fulfils predicate pred.
  Parameters:

  pred | Predicate to use in comparing the elements of the haystack and the needle(s). Mandatory if no needles are given.
  Range `doesThisStart` | The input range to check.
  Needles `withOneOfThese` | The needles against which the range is to be checked, which may be individual elements or input ranges of elements.
  R2 `withThis` | The single needle to check, which may be either a single element or an input range of elements.

  Returns:
  0 if the needle(s) do not occur at the beginning of the given range; otherwise the position of the matching needle, that is, 1 if the range starts with `withOneOfThese`[0], 2 if it starts with `withOneOfThese`[1], and so on.
  In the case where `doesThisStart` starts with multiple of the ranges or elements in `withOneOfThese`, then the shortest one matches (if there are two which match which are of the same length (e.g. "a" and 'a'), then the left-most of them in the argument list matches).
  In the case when no needle parameters are given, return true iff front of `doesThisStart` fulfils predicate pred.
  Examples:

      import std.ascii : isAlpha;

      assert("abc".startsWith!(a => a.isAlpha));
      assert("abc".startsWith!isAlpha);
      assert(!"1ab".startsWith!(a => a.isAlpha));
      assert(!"".startsWith!(a => a.isAlpha));

      import std.algorithm.comparison : among;
      assert("abc".startsWith!(a => a.among('a', 'b') != 0));
      assert(!"abc".startsWith!(a => a.among('b', 'c') != 0));

      assert(startsWith("abc", ""));
      assert(startsWith("abc", "a"));
      assert(!startsWith("abc", "b"));
      writeln(startsWith("abc", 'a', "b")); // 1
      writeln(startsWith("abc", "b", "a")); // 2
      writeln(startsWith("abc", "a", "a")); // 1
      writeln(startsWith("abc", "ab", "a")); // 2
      writeln(startsWith("abc", "x", "a", "b")); // 2
      writeln(startsWith("abc", "x", "aa", "ab")); // 3
      writeln(startsWith("abc", "x", "aaa", "sab")); // 0
      writeln(startsWith("abc", "x", "aaa", "a", "sab")); // 3

      import std.typecons : Tuple;
      alias C = Tuple!(int, "x", int, "y");
      assert(startsWith!"a.x == b"([ C(1,1), C(1,2), C(2,2) ], [1, 1]));
      writeln(startsWith!"a.x == b"([C(1, 1), C(2, 1), C(2, 2)], [1, 1], [1, 2], [1, 3])); // 2

alias `OpenRight` = std.typecons.Flag!"openRight".Flag;
  Interval option specifier for until (below) and others.
  If set to `OpenRight`.yes, then the interval is open to the right (last element is not included).
  Otherwise if set to `OpenRight`.no, then the interval is closed to the right (last element included).
Until!(pred, Range, Sentinel) `until`(alias pred = "a == b", Range, Sentinel)(Range `range`, Sentinel `sentinel`, OpenRight `openRight` = Yes.`openRight`)
if (!is(Sentinel == OpenRight));
Until!(pred, Range, void) `until`(alias pred, Range)(Range `range`, OpenRight `openRight` = Yes.`openRight`);
struct `Until`(alias pred, Range, Sentinel) if (isInputRange!Range);
  Lazily iterates `range` until the element e for which pred(e, `sentinel`) is true.
  This is similar to takeWhile in other languages.
  Parameters:

  pred | Predicate to determine when to stop.
  Range `range` | The input range to iterate over.
  Sentinel `sentinel` | The element to stop at.
  OpenRight `openRight` | Determines whether the element for which the given predicate is true should be included in the resulting range (No.`openRight`), or not (Yes.`openRight`).

  Returns:
  An input range that iterates over the original range's elements, but ends when the specified predicate becomes true. If the original range is a forward range or higher, this range will be a forward range.
  Examples:

      import std.algorithm.comparison : equal;
      import std.typecons : No;
      int[] a = [ 1, 2, 4, 7, 7, 2, 4, 7, 3, 5];
      assert(equal(a.until(7), [1, 2, 4]));
      assert(equal(a.until(7, No.openRight), [1, 2, 4, 7]));

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