ceph/src/boost/boost/json/memory_resource.hpp

   1 //
   2 // Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
   3 //
   4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 //
   7 // Official repository: https://github.com/boostorg/json
   8 //
   9
  10 #ifndef BOOST_JSON_MEMORY_RESOURCE_HPP
  11 #define BOOST_JSON_MEMORY_RESOURCE_HPP
  12
  13 #include <boost/json/detail/config.hpp>
  14
  15 #include <boost/container/pmr/memory_resource.hpp>
  16 #include <boost/container/pmr/polymorphic_allocator.hpp>
  17
  18 BOOST_JSON_NS_BEGIN
  19
  20 #ifdef BOOST_JSON_DOCS
  21
  22 /** The type of memory resource used by the library.
  23
  24     Alias for `boost::container::pmr::memory_resource`.
  25 */
  26 class memory_resource
  27 {
  28 };
  29
  30 /** The type of polymorphic allocator used by the library.
  31
  32     Alias template for `boost::container::pmr::polymorphic_allocator`.
  33 */
  34 template<class T>
  35 class polymorphic_allocator;
  36
  37 // VFALCO Bug: doc toolchain won't make this a ref
  38 //using memory_resource = __see_below__;
  39
  40 #else
  41 using memory_resource = boost::container::pmr::memory_resource;
  42
  43 template<class T>
  44 using polymorphic_allocator =
  45     boost::container::pmr::polymorphic_allocator<T>;
  46 #endif
  47
  48 /** Return true if a memory resource's deallocate function has no effect.
  49
  50     This metafunction may be specialized to indicate to
  51     the library that calls to the `deallocate` function of
  52     a @ref memory_resource have no effect. The implementation
  53     will elide such calls when it is safe to do so. By default,
  54     the implementation assumes that all memory resources
  55     require a call to `deallocate` for each memory region
  56     obtained by calling `allocate`.
  57
  58     @par Example
  59
  60     This example specializes the metafuction for `my_resource`,
  61     to indicate that calls to deallocate have no effect:
  62
  63     @code
  64
  65     // Forward-declaration for a user-defined memory resource
  66     struct my_resource;
  67
  68     // It is necessary to specialize the template from
  69     // inside the namespace in which it is declared:
  70
  71     namespace boost {
  72     namespace json {
  73
  74     template<>
  75     struct is_deallocate_trivial< my_resource >
  76     {
  77         static constexpr bool value = true;
  78     };
  79
  80     } // namespace json
  81     } // namespace boost
  82
  83     @endcode
  84
  85     It is usually not necessary for users to check this trait.
  86     Instead, they can call @ref storage_ptr::is_deallocate_trivial
  87     to determine if the pointed-to memory resource has a trivial
  88     deallocate function.
  89
  90     @see
  91         @ref memory_resource,
  92         @ref storage_ptr
  93 */
  94 template<class T>
  95 struct is_deallocate_trivial
  96 {
  97     /** A bool equal to true if calls to `T::do_deallocate` have no effect.
  98
  99         The primary template sets `value` to false.
 100     */
 101     static constexpr bool value = false;
 102 };
 103
 104 BOOST_JSON_NS_END
 105
 106 #endif