Template std.conv.to
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.
template to(T)
;
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
Contained Functions
| Name | Description |
|---|---|
| to | |
| to | |
| to |
Example
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
Example
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 stdExample
When converting strings to numeric types, note that 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);
writeln(str); // "2A"
auto i = to!int(str, 16);
writeln(i); // 42
Example
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;
writeln(to!int(to!float(a))); // a
writeln(to!int(to!float(-a))); // -a
Example
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.
import stdExample
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 stdExample
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);
Example
Object-to-object conversions by dynamic casting throw exception when the source is non-null and the target is null.
import stdExample
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, orimmutable). - Converts array (other than strings) to string.
Each element is converted by calling
to!T. - Associative array to string conversion.
Each element is converted by calling
to!T. - 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
"true"or"false". char,wchar,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 ischar*, treat it as C-style strings. In that case, this function is@system.
std on 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"Example
Strings can be converted to enum types. The enum member with the same name as the input string is returned. The comparison is case-sensitive.
A ConvException is thrown if the enum does not have the specified member.
import stdAuthors
Walter Bright, Andrei Alexandrescu, Shin Fujishiro, Adam D. Ruppe, Kenji Hara