blob: 529d5ba5bc5653cc402ddb45e8e2108beff2bbf2 [file] [log] [blame]
// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
namespace fit {
// Tag for requesting in-place initialization.
struct in_place_t {
explicit constexpr in_place_t() = default;
// Tag for requesting in-place initialization by type.
template <typename T>
struct in_place_type_t {
explicit constexpr in_place_type_t() = default;
// Tag for requesting in-place initialization by index.
template <size_t Index>
struct in_place_index_t final {
explicit constexpr in_place_index_t() = default;
#ifdef __cpp_inline_variables
// Inline variables are only available on C++ 17 and beyond.
inline constexpr in_place_t in_place{};
template <typename T>
inline constexpr in_place_type_t<T> in_place_type{};
template <size_t Index>
inline constexpr in_place_index_t<Index> in_place_index{};
// For C++ 14 we need to provide storage for the variable so we define
// a reference instead.
template <typename Dummy = void>
struct in_place_holder {
static constexpr in_place_t instance{};
template <typename T>
struct in_place_type_holder {
static constexpr in_place_type_t<T> instance{};
template <size_t Index>
struct in_place_index_holder {
static constexpr in_place_index_t<Index> instance{};
template <typename Dummy>
constexpr in_place_t in_place_holder<Dummy>::instance;
template <typename T>
constexpr in_place_type_t<T> in_place_type_holder<T>::instance;
template <size_t Index>
constexpr in_place_index_t<Index> in_place_index_holder<Index>::instance;
static constexpr const in_place_t& in_place = in_place_holder<>::instance;
template <typename T>
static constexpr const in_place_type_t<T>& in_place_type = in_place_type_holder<T>::instance;
template <size_t Index>
static constexpr const in_place_index_t<Index>& in_place_index =
#endif // __cpp_inline_variables
} // namespace fit