std::default_initializable

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Concepts library

Core language concepts same_as derived_from convertible_to common_reference_with common_with integral signed_integral unsigned_integral floating_point swappableswappable_with destructible constructible_from default_initializable move_constructible copy_constructible assignable_from

Comparison concepts equality_comparableequality_comparable_with totally_orderedtotally_ordered_with Object concepts movable copyable semiregular regular Callable concepts invocableregular_invocable predicate relation equivalence_relation strict_weak_order

 

Defined in header <concepts>
template < class T > concept default_initializable = std::constructible_from<T> && requires { T{}; } &&                                 /* T t; is well-formed, see below */;		(since C++20)

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

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