isCallable

Detect whether T is a callable object, which can be called with the function call operator $(LPAREN)...$(RPAREN).

Implicit Function Template Instantiation is *not* attempted - see below.

template isCallable (

alias callable

) {

static if(is(typeof(&callable.opCall) == delegate))

enum bool isCallable;

static if(!(is(typeof(&callable.opCall) == delegate)))

static if(is(typeof(&callable.opCall) V : V*) && is(V == function))

enum bool isCallable;

static if(!(is(typeof(&callable.opCall) == delegate)))

static if(!(is(typeof(&callable.opCall) V : V*) && is(V == function)))

static if(is(typeof(&callable.opCall!()) TemplateInstanceType))

enum bool isCallable;

static if(!(is(typeof(&callable.opCall) == delegate)))

static if(!(is(typeof(&callable.opCall) V : V*) && is(V == function)))

static if(!(is(typeof(&callable.opCall!()) TemplateInstanceType)))

static if(is(typeof(&callable!()) TemplateInstanceType))

enum bool isCallable;

static if(!(is(typeof(&callable.opCall) == delegate)))

static if(!(is(typeof(&callable.opCall) V : V*) && is(V == function)))

static if(!(is(typeof(&callable.opCall!()) TemplateInstanceType)))

static if(!(is(typeof(&callable!()) TemplateInstanceType)))

enum bool isCallable;

}

Examples

Functions, function pointers, delegates, lambdas.

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

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

auto fp = &f;
static assert( isCallable!fp);
static assert( isCallable!((int x) {}));

int x;
static assert(!isCallable!x);

Aggregate types with (static) opCall.

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);

Template functions are only detected if they are instantiable with !().

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);

static assert(!isCallable!((x) {}));

Overloaded functions and function templates instantiable with !().

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));

isCallable

Examples

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