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# std.conv

A one-stop shop for converting values from one type to another.

Category | Functions
--- | ---
Generic | castFrom emplace parse to toChars
Strings | text wtext dtext hexString
Numeric | octal roundTo signed unsigned
Exceptions | ConvException ConvOverflowException

License:
Boost License 1.0.
Authors:
Walter Bright, Andrei Alexandrescu, Shin Fujishiro, Adam D. Ruppe, Kenji Hara

Source: std/conv.d

class `ConvException`: object.Exception;
  Thrown on conversion errors.
class `ConvOverflowException`: std.conv.ConvException;
  Thrown on conversion overflow errors.
template `to`(T)
  The `to` template converts a value from one type to another. The source type is deduced and the target type must be specified, for example the expression `to`!int(42.0) converts the number 42 from double to int. The conversion is "safe", i.e., it checks for overflow; `to`!int(4.2e10) would throw the ConvOverflowException exception. Overflow checks are only inserted when necessary, e.g., `to`!double(42) does not do any checking because any int fits in a double.
  Conversions from string to numeric types differ from the C equivalents atoi() and atol() by checking for overflow and not allowing whitespace.
  For conversion of strings to signed types, the grammar recognized is:

      Integer: Sign UnsignedInteger
      UnsignedInteger
      Sign:
          +
          -

  For conversion to unsigned types, the grammar recognized is:

      UnsignedInteger:
          DecimalDigit
          DecimalDigit UnsignedInteger

  Examples:
  Converting a value to its own type (useful mostly for generic code) simply returns its argument.

      int a = 42;
      int b = to!int(a);
      double c = to!double(3.14); // c is double with value 3.14

  Examples:
  Converting among numeric types is a safe way to cast them around.
  Conversions from floating-point types to integral types allow loss of precision (the fractional part of a floating-point number). The conversion is truncating towards zero, the same way a cast would truncate. (To round a floating point value when casting to an integral, use roundTo.)

      import std.exception : assertThrown;

      int a = 420;
      assert(to!long(a) == a);
      assertThrown!ConvOverflowException(to!byte(a));

      assert(to!int(4.2e6) == 4200000);
      assertThrown!ConvOverflowException(to!uint(-3.14));
      assert(to!uint(3.14) == 3);
      assert(to!uint(3.99) == 3);
      assert(to!int(-3.99) == -3);

  Examples:
  When converting strings to numeric types, note that the D hexadecimal and binary literals are not handled. Neither the prefixes that indicate the base, nor the horizontal bar used to separate groups of digits are recognized. This also applies `to` the suffixes that indicate the type.
  To work around this, you can specify a radix for conversions involving numbers.

      auto str = to!string(42, 16);
      assert(str == "2A");
      auto i = to!int(str, 16);
      assert(i == 42);

  Examples:
  Conversions from integral types to floating-point types always succeed, but might lose accuracy. The largest integers with a predecessor representable in floating-point format are 2^24-1 for float, 2^53-1 for double, and 2^64-1 for real (when real is 80-bit, e.g. on Intel machines).

      // 2^24 - 1, largest proper integer representable as float
      int a = 16_777_215;
      assert(to!int(to!float(a)) == a);
      assert(to!int(to!float(-a)) == -a);

  Examples:
  Converting an array to another array type works by converting each element in turn. Associative arrays can be converted to associative arrays as long as keys and values can in turn be converted.

      import std.string : split;

      int[] a = [1, 2, 3];
      auto b = to!(float[])(a);
      assert(b == [1.0f, 2, 3]);
      string str = "1 2 3 4 5 6";
      auto numbers = to!(double[])(split(str));
      assert(numbers == [1.0, 2, 3, 4, 5, 6]);
      int[string] c;
      c["a"] = 1;
      c["b"] = 2;
      auto d = to!(double[wstring])(c);
      assert(d["a"w] == 1 && d["b"w] == 2);

  Examples:
  Conversions operate transitively, meaning that they work on arrays and associative arrays of any complexity.
  This conversion works because `to`!short applies to an int, `to`!wstring applies to a string, `to`!string applies to a double, and `to`!(double[]) applies to an int[]. The conversion might throw an exception because `to`!short might fail the range check.

      int[string][double[int[]]] a;
      auto b = to!(short[wstring][string[double[]]])(a);

  Examples:
  Object-`to`-object conversions by dynamic casting throw exception when the source is non-`null` and the target is `null`.

      import std.exception : assertThrown;
      // Testing object conversions
      class A {}
      class B : A {}
      class C : A {}
      A a1 = new A, a2 = new B, a3 = new C;
      assert(to!B(a2) is a2);
      assert(to!C(a3) is a3);
      assertThrown!ConvException(to!B(a3));

  Examples:
  Stringize conversion from all types is supported.
  - String to string conversion works for any two string types having (char, wchar, dchar) character widths and any combination of qualifiers (mutable, const, or immutable).
  - Converts array (other than strings) to string. Each element is converted by calling `to`!T.
  - Associative array to string conversion. Each element is printed by calling `to`!T.
  - Object to string conversion calls toString against the object or returns "`null`" if the object is `null`.
  - Struct to string conversion calls toString against the struct if it is defined.
  - For structs that do not define toString, the conversion to string produces the list of fields.
  - Enumerated types are converted to strings as their symbolic names.
  - Boolean values are printed as "`true`" or "`false`".
  - char, wchar, dchar to a string type.
  - Unsigned or signed integers to strings.
    [special case]
      Convert integral value to string in radix radix. radix must be a value from 2 `to` 36. value is treated as a signed value only if radix is 10. The characters A through Z are used `to` represent values 10 through 36 and their case is determined by the letterCase parameter.
  - All floating point types to all string types.
  - Pointer `to` string conversions prints the pointer as a size_t value. If pointer is char*, treat it as C-style strings. In that case, this function is @system.

      // Conversion representing dynamic/static array with string
      long[] a = [ 1, 3, 5 ];
      assert(to!string(a) == "[1, 3, 5]");

      // Conversion representing associative array with string
      int[string] associativeArray = ["0":1, "1":2];
      assert(to!string(associativeArray) == `["0":1, "1":2]` ||
             to!string(associativeArray) == `["1":2, "0":1]`);

      // char* to string conversion
      assert(to!string(cast(char*) null) == "");
      assert(to!string("foo\0".ptr) == "foo");

      // Conversion reinterpreting void array to string
      auto w = "abcx"w;
      const(void)[] b = w;
      assert(b.length == 8);

      auto c = to!(wchar[])(b);
      assert(c == "abcx");

template `roundTo`(Target)
  Rounded conversion from floating point to integral.
  Rounded conversions do not work with non-integral target types.
  Examples:

      assert(roundTo!int(3.14) == 3);
      assert(roundTo!int(3.49) == 3);
      assert(roundTo!int(3.5) == 4);
      assert(roundTo!int(3.999) == 4);
      assert(roundTo!int(-3.14) == -3);
      assert(roundTo!int(-3.49) == -3);
      assert(roundTo!int(-3.5) == -4);
      assert(roundTo!int(-3.999) == -4);
      assert(roundTo!(const int)(to!(const double)(-3.999)) == -4);

Target `parse`(Target, Source)(ref Source `source`)
if (isInputRange!Source && isSomeChar!(ElementType!Source) && is(Unqual!Target == bool));
  The `parse` family of functions works quite like the to family, except that:
  1. It only works with character ranges as input.
  2. It takes the input by reference. (This means that rvalues - such as string literals - are not accepted: use to instead.)
  3. It advances the input to the position following the conversion.
  4. It does not throw if it could not convert the entire input.
  This overload converts an character input range to a bool.
  Parameters:

  Target | the type to convert to
  Source `source` | the lvalue of an input range

  Returns:
  A bool
  Throws:
  A ConvException if the range does not represent a bool.

  Note: All character input range conversions using to are forwarded to `parse` and do not require lvalues.

  Examples:

      auto s = "true";
      bool b = parse!bool(s);
      assert(b);

Target `parse`(Target, Source)(ref Source `s`)
if (isSomeChar!(ElementType!Source) && isIntegral!Target && !is(Target == enum));
Target `parse`(Target, Source)(ref Source `source`, uint `radix`)
if (isSomeChar!(ElementType!Source) && isIntegral!Target && !is(Target == enum));
  Parses a character input range to an integral value.
  Parameters:

  Target | the integral type to convert to
  Source `s` | the lvalue of an input range

  Returns:
  A number of type Target
  Throws:
  A ConvException If an overflow occurred during conversion or if no character of the input was meaningfully converted.
  Examples:

      string s = "123";
      auto a = parse!int(s);
      assert(a == 123);

      // parse only accepts lvalues
      static assert(!__traits(compiles, parse!int("123")));

  Examples:

      import std.string : munch;
      string test = "123 \t  76.14";
      auto a = parse!uint(test);
      assert(a == 123);
      assert(test == " \t  76.14"); // parse bumps string
      munch(test, " \t\n\r"); // skip ws
      assert(test == "76.14");
      auto b = parse!double(test);
      assert(b == 76.14);
      assert(test == "");

Target `parse`(Target, Source)(ref Source `s`)
if (isSomeString!Source && !is(Source == enum) && is(Target == enum));
  Takes a string representing an enum type and returns that type.
  Parameters:

  Target | the enum type to convert to
  Source `s` | the lvalue of the range to parse

  Returns:
  An enum of type Target
  Throws:
  A ConvException if type Target does not have a member represented by `s`.
  Examples:

      enum EnumType : bool { a = true, b = false, c = a }

      auto str = "a";
      assert(parse!EnumType(str) == EnumType.a);

Target `parse`(Target, Source)(ref Source `source`)
if (isInputRange!Source && isSomeChar!(ElementType!Source) && !is(Source == enum) && isFloatingPoint!Target && !is(Target == enum));
  Parses a character range to a floating point number.
  Parameters:

  Target | a floating point type
  Source `source` | the lvalue of the range to parse

  Returns:
  A floating point number of type Target
  Throws:
  A ConvException if p is empty, if no number could be parsed, or if an overflow occurred.
  Examples:

      import std.math : approxEqual;
      auto str = "123.456";

      assert(parse!double(str).approxEqual(123.456));

Target `parse`(Target, Source)(ref Source `s`)
if (isSomeString!Source && !is(Source == enum) && staticIndexOf!(Unqual!Target, dchar, Unqual!(ElementEncodingType!Source)) >= 0);
Target `parse`(Target, Source)(ref Source `s`)
if (!isSomeString!Source && isInputRange!Source && isSomeChar!(ElementType!Source) && isSomeChar!Target && Target.sizeof >= ElementType!Source.sizeof && !is(Target == enum));
  Parsing one character off a range returns the first element and calls popFront.
  Parameters:

  Target | the type to convert to
  Source `s` | the lvalue of an input range

  Returns:
  A character of type Target
  Throws:
  A ConvException if the range is empty.
  Examples:

      auto s = "Hello, World!";
      char first = parse!char(s);
      assert(first == 'H');
      assert(s == "ello, World!");

Target `parse`(Target, Source)(ref Source `s`)
if (isInputRange!Source && isSomeChar!(ElementType!Source) && is(Unqual!Target == typeof(null)));
  Parsing a character range to typeof(null) returns null if the range spells "null". This function is case insensitive.
  Parameters:

  Target | the type to convert to
  Source `s` | the lvalue of an input range

  Returns:
  null
  Throws:
  A ConvException if the range doesn't represent null.
  Examples:

      import std.exception : assertThrown;

      alias NullType = typeof(null);
      auto s1 = "null";
      assert(parse!NullType(s1) is null);
      assert(s1 == "");

      auto s2 = "NUll"d;
      assert(parse!NullType(s2) is null);
      assert(s2 == "");

      auto m = "maybe";
      assertThrown!ConvException(parse!NullType(m));
      assert(m == "maybe");  // m shouldn't change on failure

      auto s = "NULL";
      assert(parse!(const NullType)(s) is null);

Target `parse`(Target, Source)(ref Source `s`, dchar `lbracket` = '[', dchar `rbracket` = ']', dchar `comma` = ',')
if (isSomeString!Source && !is(Source == enum) && isDynamicArray!Target && !is(Target == enum));
Target `parse`(Target, Source)(ref Source `s`, dchar `lbracket` = '[', dchar `rbracket` = ']', dchar `comma` = ',')
if (isExactSomeString!Source && isStaticArray!Target && !is(Target == enum));
  Parses an array from a string given the left bracket (default '['), right bracket (default ']'), and element separator (by default ','). A trailing separator is allowed.
  Parameters:

  Source `s` | The string to `parse`
  dchar `lbracket` | the character that starts the array
  dchar `rbracket` | the character that ends the array
  dchar `comma` | the character that separates the elements of the array

  Returns:
  An array of type Target
  Examples:

      auto s1 = `[['h', 'e', 'l', 'l', 'o'], "world"]`;
      auto a1 = parse!(string[])(s1);
      assert(a1 == ["hello", "world"]);

      auto s2 = `["aaa", "bbb", "ccc"]`;
      auto a2 = parse!(string[])(s2);
      assert(a2 == ["aaa", "bbb", "ccc"]);

Target `parse`(Target, Source)(ref Source `s`, dchar `lbracket` = '[', dchar `rbracket` = ']', dchar `keyval` = ':', dchar `comma` = ',')
if (isSomeString!Source && !is(Source == enum) && isAssociativeArray!Target && !is(Target == enum));
  Parses an associative array from a string given the left bracket (default '['), right bracket (default ']'), key-value separator (default ':'), and element seprator (by default ',').
  Parameters:

  Source `s` | the string to `parse`
  dchar `lbracket` | the character that starts the associative array
  dchar `rbracket` | the character that ends the associative array
  dchar `keyval` | the character that associates the key with the value
  dchar `comma` | the character that separates the elements of the associative array

  Returns:
  An associative array of type Target
  Examples:

      auto s1 = "[1:10, 2:20, 3:30]";
      auto aa1 = parse!(int[int])(s1);
      assert(aa1 == [1:10, 2:20, 3:30]);

      auto s2 = `["aaa":10, "bbb":20, "ccc":30]`;
      auto aa2 = parse!(int[string])(s2);
      assert(aa2 == ["aaa":10, "bbb":20, "ccc":30]);

      auto s3 = `["aaa":[1], "bbb":[2,3], "ccc":[4,5,6]]`;
      auto aa3 = parse!(int[][string])(s3);
      assert(aa3 == ["aaa":[1], "bbb":[2,3], "ccc":[4,5,6]]);

string `text`(T...)(T `args`)
if (T.length > 0);
wstring `wtext`(T...)(T `args`)
if (T.length > 0);
dstring `dtext`(T...)(T `args`)
if (T.length > 0);
  Convenience functions for converting one or more arguments of any type into text (the three character widths).
  Examples:

      assert( text(42, ' ', 1.5, ": xyz") == "42 1.5: xyz"c);
      assert(wtext(42, ' ', 1.5, ": xyz") == "42 1.5: xyz"w);
      assert(dtext(42, ' ', 1.5, ": xyz") == "42 1.5: xyz"d);

template `octal`(string num) if (isOctalLiteral(num))
template `octal`(alias decimalInteger) if (isIntegral!(typeof(decimalInteger)))
  The `octal` facility provides a means to declare a number in base 8. Using `octal`!177 or `octal`!"177" for 127 represented in `octal` (same as 0177 in C).
  The rules for strings are the usual for literals: If it can fit in an int, it is an int. Otherwise, it is a long. But, if the user specifically asks for a long with the L suffix, always give the long. Give an unsigned iff it is asked for with the U or u suffix. Octals created from integers preserve the type of the passed-in integral.
  See Also:
  parse for parsing `octal` strings at runtime.
  Examples:

      // same as 0177
      auto x = octal!177;
      // octal is a compile-time device
      enum y = octal!160;
      // Create an unsigned octal
      auto z = octal!"1_000_000u";

pure nothrow @safe T* `emplace`(T)(T* `chunk`);
  Given a pointer `chunk` to uninitialized memory (but already typed as T), constructs an object of non-class type T at that address. If T is a class, initializes the class reference to `null`.
  Returns:
  A pointer to the newly constructed object (which is the same as `chunk`).
  Examples:

      static struct S
      {
          int i = 42;
      }
      S[2] s2 = void;
      emplace(&s2);
      assert(s2[0].i == 42 && s2[1].i == 42);

  Examples:

      interface I {}
      class K : I {}

      K k = void;
      emplace(&k);
      assert(k is null);

      I i = void;
      emplace(&i);
      assert(i is null);

T* `emplace`(T, Args...)(T* `chunk`, auto ref Args `args`)
if (is(T == struct) || Args.length == 1);
  Given a pointer `chunk` to uninitialized memory (but already typed as a non-class type T), constructs an object of type T at that address from arguments `args`. If T is a class, initializes the class reference to `args`[0].
  This function can be @trusted if the corresponding constructor of T is @safe.
  Returns:
  A pointer to the newly constructed object (which is the same as `chunk`).
  Examples:

      int a;
      int b = 42;
      assert(*emplace!int(&a, b) == 42);

T `emplace`(T, Args...)(void[] `chunk`, auto ref Args `args`)
if (is(T == class));
  Given a raw memory area `chunk`, constructs an object of class type T at that address. The constructor is passed the arguments Args.
  If T is an inner class whose outer field can be used to access an instance of the enclosing class, then Args must not be empty, and the first member of it must be a valid initializer for that outer field. Correct initialization of this field is essential to access members of the outer class inside T methods.

  Preconditions: `chunk` must be at least as large as T needs and should have an alignment multiple of T's alignment. (The size of a class instance is obtained by using _traits(classInstanceSize, T)).

  Note: This function can be @trusted if the corresponding constructor of T is @safe.

  Returns:
  The newly constructed object.
  Examples:

      static class C
      {
          int i;
          this(int i){this.i = i;}
      }
      auto buf = new void[__traits(classInstanceSize, C)];
      auto c = emplace!C(buf, 5);
      assert(c.i == 5);

T* `emplace`(T, Args...)(void[] `chunk`, auto ref Args `args`)
if (!is(T == class));
  Given a raw memory area `chunk`, constructs an object of non-class type T at that address. The constructor is passed the arguments `args`, if any.

  Preconditions: `chunk` must be at least as large as T needs and should have an alignment multiple of T's alignment.

  Note: This function can be @trusted if the corresponding constructor of T is @safe.

  Returns:
  A pointer to the newly constructed object.
  Examples:

      struct S
      {
          int a, b;
      }
      auto buf = new void[S.sizeof];
      S s;
      s.a = 42;
      s.b = 43;
      auto s1 = emplace!S(buf, s);
      assert(s1.a == 42 && s1.b == 43);

auto `unsigned`(T)(T `x`)
if (isIntegral!T);
  Returns the corresponding unsigned value for `x` (e.g. if `x` has type int, it returns cast(uint) `x`). The advantage compared to the cast is that you do not need to rewrite the cast if `x` later changes type (e.g from int to long).
  Note that the result is always mutable even if the original type was const or immutable. In order to retain the constness, use std.traits.Unsigned.
  Examples:

      import std.traits : Unsigned;
      immutable int s = 42;
      auto u1 = unsigned(s); //not qualified
      static assert(is(typeof(u1) == uint));
      Unsigned!(typeof(s)) u2 = unsigned(s); //same qualification
      static assert(is(typeof(u2) == immutable uint));
      immutable u3 = unsigned(s); //explicitly qualified

auto `signed`(T)(T `x`)
if (isIntegral!T);
  Returns the corresponding signed value for `x` (e.g. if `x` has type uint, it returns cast(int) `x`). The advantage compared to the cast is that you do not need to rewrite the cast if `x` later changes type (e.g from uint to ulong).
  Note that the result is always mutable even if the original type was const or immutable. In order to retain the constness, use std.traits.Signed.
  Examples:

      import std.traits : Signed;

      immutable uint u = 42;
      auto s1 = signed(u); //not qualified
      static assert(is(typeof(s1) == int));
      Signed!(typeof(u)) s2 = signed(u); //same qualification
      static assert(is(typeof(s2) == immutable int));
      immutable s3 = signed(u); //explicitly qualified

template `castFrom`(From)
  A wrapper on top of the built-in cast operator that allows one to restrict casting of the original type of the value.
  A common issue with using a raw cast is that it may silently continue to compile even if the value's type has changed during refactoring, which breaks the initial assumption about the cast.
  Parameters:

  From | The type to cast from. The programmer must ensure it is legal to make this cast.

  Examples:

      // Regular cast, which has been verified to be legal by the programmer:
      {
          long x;
          auto y = cast(int) x;
      }

      // However this will still compile if 'x' is changed to be a pointer:
      {
          long* x;
          auto y = cast(int) x;
      }

      // castFrom provides a more reliable alternative to casting:
      {
          long x;
          auto y = castFrom!long.to!int(x);
      }

      // Changing the type of 'x' will now issue a compiler error,
      // allowing bad casts to be caught before it's too late:
      {
          long* x;
          static assert(
              !__traits(compiles, castFrom!long.to!int(x))
          );

          // if cast is still needed, must be changed to:
          auto y = castFrom!(long*).to!int(x);
      }

  ref @system auto `to`(To, T)(auto ref T `value`);
    Parameters:

    To | The type to cast to.
    T `value` | The `value` to cast. It must be of type From, otherwise a compile-time error is emitted.

    Returns:
    the `value` after the cast, returned by reference if possible.
template `hexString`(string hexData) if (hexData.isHexLiteral)
template `hexString`(wstring hexData) if (hexData.isHexLiteral)
template `hexString`(dstring hexData) if (hexData.isHexLiteral)
  Converts a hex literal to a string at compile time.
  Takes a string made of hexadecimal digits and returns the matching string by converting each pair of digits to a character. The input string can also include white characters, which can be used to keep the literal string readable in the source code.
  The function is intended to replace the hexadecimal literal strings starting with 'x', which could be removed to simplify the core language.
  Parameters:

  hexData | string to be converted.

  Returns:
  a string, a wstring or a dstring, according to the type of hexData.
  Examples:

      // conversion at compile time
      auto string1 = hexString!"304A314B";
      assert(string1 == "0J1K");
      auto string2 = hexString!"304A314B"w;
      assert(string2 == "0J1K"w);
      auto string3 = hexString!"304A314B"d;
      assert(string3 == "0J1K"d);

pure nothrow @nogc @safe auto `toChars`(ubyte radix = 10, Char = char, LetterCase letterCase = LetterCase.lower, T)(T `value`)
if ((radix == 2 || radix == 8 || radix == 10 || radix == 16) && (is(Unqual!T == uint) || is(Unqual!T == ulong) || radix == 10 && (is(Unqual!T == int) || is(Unqual!T == long))));
  Convert integer to a range of characters. Intended to be lightweight and fast.
  Parameters:

  radix | 2, 8, 10, 16
  Char | character type for output
  letterCase | lower for deadbeef, upper for DEADBEEF
  T `value` | integer to convert. Can be uint or ulong. If radix is 10, can also be int or long.

  Returns:
  Random access range with slicing and everything

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