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std::is_unbounded_array

Defined in header `<type_traits>`
template< class T > struct is_unbounded_array;		(since C++20)

Checks whether T is an array type of unknown bound. Provides the member constant value which is equal to true, if T is an array type of unknown bound. Otherwise, value is equal to false.

The behavior of a program that adds specializations for is_unbounded_array or is_unbounded_array_v is undefined.

Template parameters

a type to check

Helper variable template

template< class T >
inline constexpr bool is_unbounded_array_v = is_unbounded_array<T>::value;

(since C++20)

Inherited from std::integral_constant

Member constants

value

[static]

true if T is an array type of unknown bound, 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>

Possible implementation

template<class T>
struct is_unbounded_array: std::false_type {};
 
template<class T>
struct is_unbounded_array<T[]> : std::true_type {};

Notes

Feature-test macro
`__cpp_lib_bounded_array_traits`

Example

#include <iostream>
#include <type_traits>
 
#define OUT(...) std::cout << #__VA_ARGS__ << " : " << __VA_ARGS__ << '\n'
 
class A {};
 
int main()
{
    std::cout << std::boolalpha;
    OUT( std::is_unbounded_array_v<A> );
    OUT( std::is_unbounded_array_v<A[]> );
    OUT( std::is_unbounded_array_v<A[3]> );
    OUT( std::is_unbounded_array_v<float> );
    OUT( std::is_unbounded_array_v<int> );
    OUT( std::is_unbounded_array_v<int[]> );
    OUT( std::is_unbounded_array_v<int[3]> );
}

Output:

std::is_unbounded_array_v<A> : false
std::is_unbounded_array_v<A[]> : true
std::is_unbounded_array_v<A[3]> : false
std::is_unbounded_array_v<float> : false
std::is_unbounded_array_v<int> : false
std::is_unbounded_array_v<int[]> : true
std::is_unbounded_array_v<int[3]> : false

is_array (C++11)	checks if a type is an array type (class template)
is_bounded_array (C++20)	checks if a type is an array type of known bound (class template)
extent (C++11)	obtains the size of an array type along a specified dimension (class template)