std.conv
A one-stop shop for converting values from one type to another.
- class ConvError: object.Error;
- Thrown on conversion errors.
- class ConvOverflowError: object.Error;
- Thrown on conversion overflow errors.
- template to(Target)
- The to family of functions converts a value from type
Source to type Target. 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
ConvOverflowError 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.
Converting a value to its own type (useful mostly for generic code)
simply returns its argument.
Example:
int a = 42;
auto b = to!(int)(a); auto c = to!(double)(3.14);
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.)
Examples:
int a = 420;
auto b = to!(long)(a); auto c = to!(byte)(a / 10); auto d = to!(byte)(a); double e = 4.2e6;
auto f = to!(int)(e); e = -3.14;
auto g = to!(uint)(e); e = 3.14;
auto h = to!(uint)(e); e = 3.99;
h = to!(uint)(a); e = -3.99;
f = to!(int)(a);
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).
Example:
int a = 16_777_215; assert(to!(int)(to!(float)(a)) == a);
assert(to!(int)(to!(float)(-a)) == -a);
a += 2;
assert(to!(int)(to!(float)(a)) == a);
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
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.
Example:
int[] a = ([1, 2, 3]).dup;
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);
Conversions operate transitively, meaning that they work on arrays and
associative arrays of any complexity:
int[string][double[int[]]] a;
...
auto b = to!(short[wstring][string[double[]]])(a);
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.
- template roundTo(Target)
- Rounded conversion from floating point to integral.
Example:
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);
Rounded conversions do not work with non-integral target types.
- template parse(Target)
- The parse family of functions works quite like the
to family, except that (1) it only works with strings as
input, (2) takes the input string by reference and advances it to
the position following the conversion, and (3) does not throw if it
could not convert the entire string. It still throws if an overflow
occurred during conversion or if no character of the input string
was meaningfully converted.
Example:
string test = "123 \t 76.14";
auto a = parse!(uint)(test);
assert(a == 123);
assert(test == " \t 76.14"); munch(test, " \t\n\r"); assert(test == "76.14");
auto b = parse!(double)(test);
assert(b == 76.14);
assert(test == "");
- int toInt(string s);
uint toUint(string s);
long toLong(string s);
ulong toUlong(string s);
short toShort(string s);
ushort toUshort(string s);
byte toByte(string s);
ubyte toUbyte(string s);
float toFloat(Char)(Char[] s);
double toDouble(Char)(Char[] s);
real toReal(Char)(Char[] s);
- Convert character string to the return type. These functions will be
deprecated because to!(T) supersedes them.