Boost C++ Libraries

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is_empty

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 from true_type.

is_empty<empty_class const>::type is the type true_type.

is_empty<empty_class>::value is an integral constant expression that evaluates to true.

is_empty<T>::value_type is the type bool.


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