| [/ |
| Copyright 2018 Glen Joseph Fernandes |
| (glenjofe@gmail.com) |
| |
| 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:enable_if enable_if_] |
| |
| template<bool B, class T = void> |
| struct enable_if_; |
| |
| template<bool B, class T = void> |
| using enable_if_t = typename enable_if_<B, T>::type; |
| |
| __type If `B` is true, then the member `type` is defined to be `T`. Otherwise |
| there is no member `type`. |
| |
| __header `#include <boost/type_traits/enable_if.hpp>` |
| |
| [note The trait has the name `enable_if_` (with a trailing underscore) but |
| behaves like `std::enable_if` or `boost::enable_if_c`. The existing trait |
| with the name `boost::enable_if` has a different interface.] |
| |
| __examples |
| |
| The following function can be used to destroy each element of an array and |
| specially handle arrays of trivially destructible types. |
| |
| template<class T> |
| typename boost::enable_if_<!boost::has_trivial_destructor<T>::value>::type |
| destroy(T* ptr, std::size_t size) |
| { |
| while (size > 0) { |
| ptr[--size].~T(); |
| } |
| } |
| |
| template<class T> |
| typename boost::enable_if_<boost::has_trivial_destructor<T>::value>::type |
| destroy(T*, std::size_t) { } |
| |
| [all_compilers] The type alias `enable_if_t` is only available if the compiler |
| supports template aliases. |
| |
| [endsect] |
