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Enum member std.traits.isCallable

Detect whether T is a callable object, which can be called with the function call operator class="pln">LPAREN...class="pln">RPAREN.

enum isCallable(alias callable) = true;

Example

Functions, lambdas, and aggregate types with (static) opCall. 

void f() { }
int g(int x) { return x; }

static assert( isCallable!f);
static assert( isCallable!g);

class C { int opCall(int) { return 0; } }
auto c = new C;
struct S { static int opCall(int) { return 0; } }
interface I { real value() @property; }

static assert( isCallable!c);
static assert( isCallable!(c.opCall));
static assert( isCallable!S);
static assert( isCallable!(I.value));
static assert( isCallable!((int a) { return a; }));

static assert(!isCallable!I);

Example

Templates 

void f()() { }
T g(T = int)(T x) { return x; }
struct S1 { static void opCall()() { } }
struct S2 { static T opCall(T = int)(T x) {return x; } }

static assert( isCallable!f);
static assert( isCallable!g);
static assert( isCallable!S1);
static assert( isCallable!S2);

Example

Overloaded functions and function templates. 

static struct Wrapper
{
    void f() { }
    int f(int x) { return x; }

    void g()() { }
    T g(T = int)(T x) { return x; }
}

static assert(isCallable!(Wrapper.f));
static assert(isCallable!(Wrapper.g));

Authors

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

License

Boost License 1.0.