std::is_unbounded_array

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

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

#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() {}

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)
is_unbounded_array_type (C++26)	checks if reflection represents an array type of unknown bound (function)

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