#include <utility>

struct BadOptionalAccess {
};

template <typename T>
class Optional {
private:
    // alignas нужен для правильного выравнивания блока памяти
    alignas(T) unsigned char data[sizeof(T)];
    bool defined;

public:
    Optional(): defined(false) {}
    Optional(const T& elem): defined(true) {
        new (data) T(elem);
    }
    Optional(T && elem): defined(true) {
        new (data) T(std::move(elem));
    }
    Optional(const Optional& other): defined(other.has_value()) {
        if (other.has_value())
            new (data) T(other.value());
    }

    Optional& operator=(const Optional& other) {
        if (other.has_value()) {
            if (!defined)
                new (data) T(other.value());
            else
                (**this) = other.value();
            defined = true;
        } else {
            reset();
        }
        return *this;
    }
    Optional& operator=(const T& elem) {
        if (!defined)
            new (data) T(elem);
        else
            (**this) = elem;
        defined = true;
        return *this;
    }
    Optional& operator=(T&& elem) {
        if (!defined)
            new (data) T(std::move(elem));
        else
            (**this) = std::move(elem);
        defined = true;
        return *this;
    }

    bool has_value() const {
        return defined;
    }

    T& operator*() {
        return *reinterpret_cast<T*>(data);
    }
    const T& operator*() const {
        return *reinterpret_cast<const T*>(data);
    }

    T* operator->() {
        return reinterpret_cast<T*>(data);
    }
    const T* operator->() const {
        return reinterpret_cast<const T*>(data);
    }

    T& value() {
        if (!defined)
            throw BadOptionalAccess();
        return (**this);
    }
    const T& value() const {
        if (!defined)
            throw BadOptionalAccess();
        return (**this);
    }

    void reset() {
        if (defined)
            reinterpret_cast<T*>(data)->~T();
        defined = false;
    }

    ~Optional() {
        reset();
    }
};