libs/type_traits/doc/is_empty.qbk
[/ Copyright 2007 John Maddock. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt). ] [section:is_empty is_empty] template <class T> struct is_empty : public __tof {}; __inherit If T is an empty class type then inherits from __true_type, otherwise inherits from __false_type. __std_ref 10p5. __header ` #include <boost/type_traits/is_empty.hpp>` or ` #include <boost/type_traits.hpp>` __compat In order to correctly detect empty classes this trait relies on either: * the compiler implementing zero sized empty base classes, or * the compiler providing __intrinsics to detect empty classes. 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`.] [endsect]