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- [/
- 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 (and not a union 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 - this latter case can be tested for
- by checking to see if the macro BOOST_IS_EMPTY is defined.
- Can not be used with incomplete 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]
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