std:: is_unbounded_array

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

std::is_unbounded_array is a UnaryTypeTrait .

Checks whether T is an arrays 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 .

If the program adds specializations for std::is_unbounded_array or std::is_unbounded_array_v , the behavior is undefined.

Template parameters

T - a type to check

Helper variable template

template < class T >
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 Value Std Feature
__cpp_lib_bounded_array_traits 201902L (C++20) std::is_bounded_array , std::is_unbounded_array

Example

Run this code 
#include <type_traits>
 
class A {};
 
static_assert
(""
    && 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
);
 
int main() {}

See also

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