97 lines
1.8 KiB
C++
97 lines
1.8 KiB
C++
// SPDX-License-Identifier: BSD-2-Clause
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// author: Max Kellermann <max.kellermann@gmail.com>
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#pragma once
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#include <cassert>
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#include <new>
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#include <type_traits>
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#include <utility>
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/**
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* Container for an object that gets constructed and destructed
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* manually. The object is constructed in-place, and therefore
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* without allocation overhead. It can be constructed and destructed
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* repeatedly.
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*/
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template<class T>
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class Manual {
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using Storage = std::aligned_storage_t<sizeof(T), alignof(T)>;
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Storage storage;
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#ifndef NDEBUG
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bool initialized = false;
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#endif
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public:
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using value_type = T;
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using reference = T &;
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using const_reference = const T &;
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using pointer = T *;
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using const_pointer = const T *;
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#ifndef NDEBUG
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~Manual() noexcept {
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assert(!initialized);
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}
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#endif
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/**
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* Cast a value reference to the containing Manual instance.
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*/
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static constexpr Manual<T> &Cast(reference value) noexcept {
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return reinterpret_cast<Manual<T> &>(value);
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}
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template<typename... Args>
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void Construct(Args&&... args) {
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assert(!initialized);
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::new(&storage) T(std::forward<Args>(args)...);
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#ifndef NDEBUG
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initialized = true;
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#endif
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}
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void Destruct() noexcept {
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assert(initialized);
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reference t = Get();
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t.T::~T();
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#ifndef NDEBUG
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initialized = false;
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#endif
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}
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reference Get() noexcept {
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assert(initialized);
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return *std::launder(reinterpret_cast<pointer>(&storage));
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}
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const_reference Get() const noexcept {
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assert(initialized);
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return *std::launder(reinterpret_cast<const_pointer>(&storage));
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}
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operator reference() noexcept {
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return Get();
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}
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operator const_reference() const noexcept {
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return Get();
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}
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pointer operator->() noexcept {
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return &Get();
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}
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const_pointer operator->() const noexcept {
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return &Get();
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}
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};
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