std::is_function
From cppreference.com
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) |
operator()
(C++14)
|
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
Run this code
#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) |
(C++11)
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checks if a type is a class type (but not union type) (class template) |
(library fundamentals TS)
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variable template alias of std::is_function::value (variable template) |