...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
template <class T>
struct is_empty : public true_type-or-false_type
{};
Inherits: If T is an empty class type then inherits from true_type, otherwise inherits from false_type.
C++ Standard Reference: 10p5.
Header: #include
<boost/type_traits/is_empty.hpp>
or #include <boost/type_traits.hpp>
Compiler Compatibility: In order to correctly detect empty classes this trait relies on either:
Can not be used with incomplete types.
Can not be used with union types, until is_union can be made to work.
If the compiler does not support partial-specialization of class templates, then this template can not be used with abstract types.
Examples:
Given:
struct empty_class {};
is_empty<empty_class>
inherits fromtrue_type
.
is_empty<empty_class const>::type
is the typetrue_type
.
is_empty<empty_class>::value
is an integral constant expression that evaluates to true.
is_empty<T>::value_type
is the typebool
.