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version 2.109.1

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Struct std.typecons.Typedef

Typedef allows the creation of a unique type which is based on an existing type. Unlike the alias feature, Typedef ensures the two types are not considered as equals.

struct Typedef(T, T init = T.init, string cookie = null) ;

Methods

NameDescription
toString () Convert wrapped value to a human readable string

Parameters

NameDescription
init Optional initial value for the new type.
Optional, used to create multiple unique types which are based on the same origin type T

Note

If a library routine cannot handle the Typedef type, you can use the TypedefType template to extract the type which the Typedef wraps.

Example

alias MyInt = Typedef!int;
MyInt foo = 10;
foo++;
writeln(foo); // 11

Example

custom initialization values 

alias MyIntInit = Typedef!(int, 42);
static assert(is(TypedefType!MyIntInit == int));
static assert(MyIntInit() == 42);

Example

Typedef creates a new type 

alias MyInt = Typedef!int;
static void takeInt(int) {}
static void takeMyInt(MyInt) {}

int i;
takeInt(i);    // ok
static assert(!__traits(compiles, takeMyInt(i)));

MyInt myInt;
static assert(!__traits(compiles, takeInt(myInt)));
takeMyInt(myInt);  // ok

Example

Use the optional cookie argument to create different types of the same base type 

alias TypeInt1 = Typedef!int;
alias TypeInt2 = Typedef!int;

// The two Typedefs are the same type.
static assert(is(TypeInt1 == TypeInt2));

alias MoneyEuros = Typedef!(float, float.init, "euros");
alias MoneyDollars = Typedef!(float, float.init, "dollars");

// The two Typedefs are _not_ the same type.
static assert(!is(MoneyEuros == MoneyDollars));

Authors

Andrei Alexandrescu, Bartosz Milewski, Don Clugston, Shin Fujishiro, Kenji Hara

License

Boost License 1.0.