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
to!int(42.0) converts the number 42 from
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
template to(T) ;
Conversions from string to numeric types differ from the C equivalents
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 a value to its own type (useful mostly for generic code) simply returns its argument.
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
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.
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
real is 80-bit, e.g. on Intel machines).
Conversion from string types to char types enforces the input
to consist of a single code point, and said code point must
fit in the target type. Otherwise,
ConvException is thrown.
.exception : assertThrown; writeln(to!char("a")); // 'a' assertThrown(to!char("ñ")); // 'ñ' does not fit into a char writeln(to!wchar("ñ")); // 'ñ' assertThrown(to!wchar("😃")); // '😃' does not fit into a wchar writeln(to!dchar("😃")); // '😃' // Using wstring or dstring as source type does not affect the result writeln(to!char("a"w)); // 'a' writeln(to!char("a"d)); // 'a' // Two code points cannot be converted to a single one assertThrown(to!char("ab"));
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.
.string : split; int a = [1, 2, 3]; auto b = to!(float)(a); writeln(b); // [1.0f, 2, 3] string str = "1 2 3 4 5 6"; auto numbers = to!(double)(split(str)); writeln(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.
This conversion works because
to!short applies to an
applies to a
to!string applies to a
to!(double) applies to an
int. The conversion might throw an
to!short might fail the range check.
Object-to-object conversions by dynamic casting throw exception when the source is non-null and the target is null.
Stringize conversion from all types is supported.
- String to string conversion works for any two string types having
dchar) character widths and any combination of qualifiers (mutable,
- Converts array (other than strings) to string.
Each element is converted by calling
- Associative array to string conversion.
Each element is converted by calling
- Object to string conversion calls
toStringagainst the object or returns
"null"if the object is null.
- Struct to string conversion calls
toStringagainst 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 converted to
dcharto 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 convert the pointer to a
size_tvalue. If pointer is
char*, treat it as C-style strings. In that case, this function is
stdon how toString should be defined.
// Conversion representing dynamic/static array with string long a = [ 1, 3, 5 ]; writeln(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 writeln(to!string(cast(char*)null)); // "" writeln(to!string("foo\0"
.ptr)); // "foo" // Conversion reinterpreting void array to string auto w = "abcx"w; const(void) b = w; writeln(b .length); // 8 auto c = to!(wchar)(b); writeln(c); // "abcx"