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`std.traits.Select/select` - multiple declarations

Function select

If cond is true, returns a without evaluating b. Otherwise, returns b without evaluating a.


						
				A select(bool cond : true, A, B)
				(
				

				  A a,
				

				  lazy B b
				

				);
				

				

				B select(bool cond : false, A, B)
				(
				

				  lazy A a,
				

				  B b
				

				);

Alias Select

Aliases itself to T[0] if the boolean condition is true and to T[1] otherwise.


						
				alias Select(bool condition, T...)
				 = Alias!(T[!condition]);

Example

// can select types
static assert(is(Select!(true, int, long) == int));
static assert(is(Select!(false, int, long) == long));
static struct Foo {}
static assert(is(Select!(false, const(int), const(Foo)) == const(Foo)));

// can select symbols
int a = 1;
int b = 2;
alias selA = Select!(true, a, b);
alias selB = Select!(false, a, b);
writeln(selA); // 1
writeln(selB); // 2

// can select (compile-time) expressions
enum val = Select!(false, -4, 9 - 6);
static assert(val == 3);
}

/**
If <code class="lang-d"><span class="pln">cond</span></code> is <code class="lang-d"><span class="kwd">true</span></code>, returns <code class="lang-d"><span class="pln">a</span></code> without evaluating <code class="lang-d"><span class="pln">b</span></code>. Otherwise, returns <code class="lang-d"><span class="pln">b</span></code> without evaluating <code class="lang-d"><span class="pln">a</span></code>.
*/
A select(bool cond : true, A, B)(A a, lazy B b) { return a;

Authors

Walter Bright, Tomasz Stachowiak (isExpressions), Andrei Alexandrescu, Shin Fujishiro, Robert Clipsham, David Nadlinger, Kenji Hara, Shoichi Kato

License

Boost License 1.0.