Scroll to navigation

std::default_initializable(3) C++ Standard Libary std::default_initializable(3)


std::default_initializable - std::default_initializable


Defined in header <concepts>
template < class T >

concept default_initializable = std::constructible_from<T> && (since C++20)
requires { T{}; } &&

/* T t; is well-formed, see below */;

The default_initializable concept checks whether variables of type T can be

* value-initialized (T() is well-formed);
* direct-list-initialized from an empty initializer list (T{} is well-formed); and
* default-initialized (T t; is well-formed).

Access checking is performed as if in a context unrelated to T. Only the validity of
the immediate context of the variable initialization is considered.

Possible implementation

template<class T>
concept default_initializable =
std::constructible_from<T> &&
requires { T{}; } &&
requires { ::new (static_cast<void*>(nullptr)) T; };

See also

specifies that a variable of the type can be
constructible_from constructed from or bound to a set of argument
(C++20) types
is_nothrow_default_constructible checks if a type has a default constructor
(C++11) (class template)