movable_box.h

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#pragma once
 
#include "di/meta/operations.h"
#include "di/meta/trivial.h"
#include "di/meta/util.h"
#include "di/meta/vocab.h"
#include "di/types/in_place.h"
#include "di/util/addressof.h"
#include "di/util/construct_at.h"
#include "di/util/destroy_at.h"
#include "di/util/forward.h"
#include "di/util/initializer_list.h"
#include "di/util/move.h"
#include "di/util/swap.h"
 
namespace di::util {
template<concepts::DefaultConstructible T>
requires(!concepts::MoveConstructible<T>)
class MovableBox {
public:
    MovableBox() = default;
 
    MovableBox(MovableBox const&) = delete;
    constexpr MovableBox(MovableBox&&) : MovableBox() {}
 
    auto operator=(MovableBox const&) -> MovableBox& = delete;
    auto operator=(MovableBox&&) -> MovableBox& = delete;
 
    template<typename... Args>
    requires(concepts::ConstructibleFrom<T, Args...>)
    constexpr explicit MovableBox(types::InPlace, Args&&... args) : m_value(util::forward<Args>(args)...) {}
 
    constexpr auto value() & -> T& { return m_value; }
    constexpr auto value() const& -> T const& { return m_value; }
    constexpr auto value() && -> T&& { return util::move(m_value); }
    constexpr auto value() const&& -> T const&& { return util::move(m_value); }
 
private:
    T m_value {};
};
}
 
namespace di {
using util::MovableBox;
}