boost/json/is_deallocate_trivial.hpp

0001 //
0002 // Copyright (c) 2024 Dmitry Arkhipov (grisumbras@yandex.ru)
0003 //
0004 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0005 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 //
0007 // Official repository: https://github.com/boostorg/json
0008 //
0009
0010 #ifndef BOOST_JSON_IS_DEALLOCATE_TRIVIAL_HPP
0011 #define BOOST_JSON_IS_DEALLOCATE_TRIVIAL_HPP
0012
0013 namespace boost {
0014 namespace json {
0015
0016 /** Return true if a memory resource's deallocate function has no effect.
0017
0018     This metafunction may be specialized to indicate to the library that calls
0019     to the `deallocate` function of a `boost::container::pmr::memory_resource`
0020     have no effect. The implementation will elide such calls when it is safe to
0021     do so. By default, the implementation assumes that all memory resources
0022     require a call to `deallocate` for each memory region obtained by
0023     calling `allocate`.
0024
0025     @par Example
0026
0027     This example specializes the metafuction for `my_resource`,
0028     to indicate that calls to deallocate have no effect:
0029
0030     @code
0031
0032     // Forward-declaration for a user-defined memory resource
0033     struct my_resource;
0034
0035     // It is necessary to specialize the template from
0036     // inside the namespace in which it is declared:
0037
0038     namespace boost {
0039     namespace json {
0040
0041     template<>
0042     struct is_deallocate_trivial< my_resource >
0043     {
0044         static constexpr bool value = true;
0045     };
0046
0047     } // namespace json
0048     } // namespace boost
0049
0050     @endcode
0051
0052     It is usually not necessary for users to check this trait.
0053     Instead, they can call @ref storage_ptr::is_deallocate_trivial
0054     to determine if the pointed-to memory resource has a trivial
0055     deallocate function.
0056
0057     @see
0058         @ref storage_ptr,
0059         @ref boost::container::pmr::memory_resource
0060 */
0061 template<class T>
0062 struct is_deallocate_trivial
0063 {
0064     /** A bool equal to true if calls to `T::do_deallocate` have no effect.
0065
0066         The primary template sets `value` to false.
0067     */
0068     static constexpr bool value = false;
0069 };
0070
0071 } // namespace json
0072 } // namespace boost
0073
0074 #endif // BOOST_JSON_IS_DEALLOCATE_TRIVIAL_HPP