C++ linear types by Ivan Cukic from Meeting C++ 2018 Secret Lightning talks

linear_types.hpp

#include <type_traits>
#include <utility>

namespace detail {

    template <typename T, typename U>
    constexpr bool linear_usable_as_v =
        std::is_nothrow_constructible_v<T, U> &&
        std::is_nothrow_assignable_v<T&, U> &&
        std::is_nothrow_convertible_v<U, T>;

    template <typename T, typename U>
    constexpr bool linear_unusible_as_v =
        !std::is_constructible_v<T, U> &&
        !std::is_assignable_v<T&, U> &&
        !std::is_convertible_v<U, T>;

}

template <typename T>
concept Linear =
    std::is_nothrow_destructible_v<T> &&

    detail::linear_usable_as_v<T, T> &&
    detail::linear_usable_as_v<T, T&&> &&

    detail::linear_unusible_as_v<T, T&> &&
    detail::linear_unusible_as_v<T, T const &> &&
    detail::linear_unusible_as_v<T, const T>;


template <typename T>
class linear_wrapper {
public:
    linear_wrapper(T && value) : value_(value) {}
    
    linear_wrapper(linear_wrapper const &) = delete;
    linear_wrapper(linear_wrapper &&) noexcept = default;

    linear_wrapper& operator=(linear_wrapper const &) = delete;
    linear_wrapper& operator=(linear_wrapper &&) noexcept = default;

    [[nodiscard]] T&& get() && noexcept { return std::move(value_); }

private:
    T value_;
};