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version 2.109.0

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Alias std.meta.Alias

Allows aliasing of any single symbol, type or compile-time expression.

alias Alias(alias a) = a;
alias Alias(T) = T;

Not everything can be directly aliased. An alias cannot be declared of - for example - a literal: 

alias a = 4; //Error

With this template any single entity can be aliased: 

alias b = Alias!4; //OK

See Also

To alias more than one thing at once, use AliasSeq.

Example

// Without Alias this would fail if Args[0] was e.g. a value and
// some logic would be needed to detect when to use enum instead
alias Head(Args...) = Alias!(Args[0]);
alias Tail(Args...) = Args[1 .. $];

alias Blah = AliasSeq!(3, int, "hello");
static assert(Head!Blah == 3);
static assert(is(Head!(Tail!Blah) == int));
static assert((Tail!Blah)[1] == "hello");

Example

alias a = Alias!(123);
static assert(a == 123);

enum abc = 1;
alias b = Alias!(abc);
static assert(b == 1);

alias c = Alias!(3 + 4);
static assert(c == 7);

alias concat = (s0, s1) => s0 ~ s1;
alias d = Alias!(concat("Hello", " World!"));
static assert(d == "Hello World!");

alias e = Alias!(int);
static assert(is(e == int));

alias f = Alias!(AliasSeq!(int));
static assert(!is(typeof(f[0]))); //not an AliasSeq
static assert(is(f == int));

auto g = 6;
alias h = Alias!g;
++h;
writeln(g); // 7

Authors

Walter Bright, David Nadlinger

License

Boost License 1.0.