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std::is_function

From cppreference.com
< cpp‎ | types
 
 
 
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is_function
(C++11)
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Defined in header <type_traits>
template< class T >
struct is_function;
(since C++11)

Checks whether T is a function type (not std::function). Provides the member constant value which is equal to true, if T is a function type. Otherwise, value is equal to false.

Contents

[edit] Template parameters

T - a type to check

Inherited from std::integral_constant

Member constants

value
[static]
true if T is a function type , false otherwise
(public static member constant)

Member functions

operator bool
converts the object to bool, returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

[edit] Possible implementation

// primary template
template<class>
struct is_function : std::false_type { };
 
// specialization for regular functions
template<class Ret, class... Args>
struct is_function<Ret(Args...)> : std::true_type {};
 
// specialization for variadic functions such as std::printf
template<class Ret, class... Args>
struct is_function<Ret(Args......)> : std::true_type {};
 
// specialization for function types that have cv-qualifiers
template<class Ret, class... Args>
struct is_function<Ret(Args...)const> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)volatile> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)const volatile> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)const> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)volatile> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)const volatile> : std::true_type {};
 
// specialization for function types that have ref-qualifiers
template<class Ret, class... Args>
struct is_function<Ret(Args...) &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)const &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)volatile &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)const volatile &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......) &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)const &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)volatile &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)const volatile &> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...) &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)const &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)volatile &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args...)const volatile &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......) &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)const &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)volatile &&> : std::true_type {};
template<class Ret, class... Args>
struct is_function<Ret(Args......)const volatile &&> : std::true_type {};

[edit] Example

#include <iostream>
#include <type_traits>
 
struct A {};
 
int f()
{
    return 1;
}
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_function<A>::value << '\n';
    std::cout << std::is_function<int(int)>::value << '\n';
    std::cout << std::is_function<decltype(f)>::value << '\n';
    std::cout << std::is_function<int>::value << '\n';
}

Output:

false
true
true
false

[edit] See also

(C++11)
checks if a type is object type
(class template) [edit]
(C++11)
checks if a type is a class type (but not union type)
(class template) [edit]