C++ named requirements: DefaultConstructible

Specifies that an instance of the type can be default constructed.

Requirements

The type T satisfies DefaultConstructible if
Given

• u, an arbitrary identifier

The following expressions must be valid and have their specified effects

pub	Expression	Post-conditions
pub	T u;	The object u is default-initialized
pub	T u;	The object u is value-initialized or aggregate-initialized
pub	T() T{}	A temporary object of type T is value-initialized or aggregate-initialized

Notes

For objects of non-aggregate class type, a public default constructor must be defined (either user-defined or implicitly defined) to satisfy DefaultConstructible.

Non-const objects of non-class object type are always DefaultConstructible.

Const non-class types are not DefaultConstructible.

Const aggregate types are not DefaultConstructible if any of their members is an object of non-class type.

Non-object types (function types, reference types, and the (possibly cv-qualified) type void) as well as the const non-object types are never DefaultConstructible

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 724	C++98	the requirements of DefaultConstructible were missing	added