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...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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is_function

template <class T>
struct is_function : public true_type-or-false_type {};

Inherits: If T is a (possibly cv-qualified) function type then inherits from true_type, otherwise inherits from false_type. Note that this template does not detect pointers to functions, or references to functions, these are detected by is_pointer and is_reference respectively:

typedef int f1();      // f1 is of function type.
typedef int (*f2)();   // f2 is a pointer to a function.
typedef int (&f3)();   // f3 is a reference to a function.

C++ Standard Reference: 3.9.2p1 and 8.3.5.

Header: #include <boost/type_traits/is_function.hpp> or #include <boost/type_traits.hpp>

Examples:

is_function<int (void)> inherits from true_type.

is_function<long (double, int)>::type is the type true_type.

is_function<long (double, int)>::value is an integral constant expression that evaluates to true.

is_function<long (*)(double, int)>::value is an integral constant expression that evaluates to false: the argument in this case is a pointer type, not a function type.

is_function<long (&)(double, int)>::value is an integral constant expression that evaluates to false: the argument in this case is a reference to a function, not a function type.

is_function<long (MyClass::*)(double, int)>::value is an integral constant expression that evaluates to false: the argument in this case is a pointer to a member function.

is_function<T>::value_type is the type bool.

[Tip] Tip

Don't confuse function-types with pointers to functions:

typedef int f(double);

defines a function type,

f foo;

declares a prototype for a function of type f,

f* pf = foo;

f& fr = foo;

declares a pointer and a reference to the function foo.

If you want to detect whether some type is a pointer-to-function then use:

is_function<remove_pointer<T>::type>::value && is_pointer<T>::value

or for pointers to member functions you can just use is_member_function_pointer directly.


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