Спринт 14. Variadic Templates. Задание 3.

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optional.h
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#include <stdexcept>
#include <utility>

class BadOptionalAccess : public std::exception {
public:
    using exception::exception;

    virtual const char* what() const noexcept override {
        return "Bad optional access";
    }
};

template <typename T>
class Optional {
public:

    Optional() = default;

    Optional(const T& item) {
        buff_ = new (&data_[0]) T(item);

        is_initialized_ = true;
    }

    Optional(T&& item) {
        buff_ = new (&data_[0]) T(std::forward<T>(item));

        is_initialized_ = true;
    }

    Optional(const Optional& other) {

        (!other.HasValue() && HasValue()) ? Reset() :
        (other.HasValue() && !this->HasValue()) ? (void)(buff_ = new (&data_[0]) T(other.Value()), is_initialized_ = true) :
        (other.HasValue() && HasValue()) ? (void)(*buff_ = other.Value(), is_initialized_ = true) : void();

    }

    Optional(Optional&& other) noexcept {

        (!other.HasValue() && this->HasValue()) ? Reset() :
        (other.HasValue() && !HasValue()) ? (void)(buff_ = new (&data_[0]) T(std::forward<T>(other.Value())), is_initialized_ = true) :
        (other.HasValue() && HasValue()) ? (void)(*buff_ = std::forward<T>(other.Value()), is_initialized_ = true) : void();

    }

    ~Optional() {
        is_initialized_ ? buff_->~T() : void();
    }

    bool HasValue() const {return is_initialized_;}
    T& Value() {if (!is_initialized_) {throw BadOptionalAccess();} else {return *buff_;}}
    const T& Value() const {if (!is_initialized_) {throw BadOptionalAccess();} else {return *buff_;}}

    void Reset() {is_initialized_ ? (is_initialized_ = false, buff_->~T()) : void();}

    template <typename ... Args>
    void Emplace(Args&& ...args);

    Optional& operator=(const T& item) {

        HasValue() ? (void)(*buff_ = item ) : (void)(buff_ = new (&data_[0]) T(item), is_initialized_ = true);

        return *this;
    }

    Optional& operator=(T&& item) {

        HasValue() ? (void)(*buff_ = std::forward<T>(item))
        : (void)(buff_ = new (&data_[0]) T(std::forward<T>(item)), is_initialized_ = true);

        return *this;
    }

    Optional& operator=(const Optional& other) {

        (!other.HasValue() && HasValue()) ? Reset() :
        (other.HasValue() && !HasValue()) ? (void)(buff_ = new (&data_[0]) T(other.Value()), is_initialized_ = true) :
        (other.HasValue() && HasValue()) ? (void)(*buff_ = other.Value(), is_initialized_ = true) : void();

        return *this;
    }

    Optional& operator=(Optional&& other) noexcept {

        (!other.HasValue() && HasValue()) ? Reset() :
        (other.HasValue() && !HasValue()) ? (void)(buff_ = new (&data_[0]) T(std::forward<T>(other.Value())), is_initialized_ = true) :
        (other.HasValue() && HasValue()) ? (void)(*buff_ = std::forward<T>(other.Value()), is_initialized_ = true) : void();

        return *this;
    }

    T& operator*() {return Value();}
    const T& operator*() const {return Value();}
    T* operator->() {return &Value();}
    const T* operator->() const {return &Value();}

private:
    T* buff_ = nullptr;

    alignas(T) char data_[sizeof(T)]{};
    bool is_initialized_ = false;
};

template <typename T>
template <typename ... Args>
void Optional<T>::Emplace(Args&& ...args) {

    if (is_initialized_) {buff_->~T();}

    buff_ = new (&data_[0]) T(std::forward<Args>(args)...);
    is_initialized_ = true;
}
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main.cpp
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#include "optional.h"

#include <cassert>
#include <memory>

struct C {
    C() noexcept {++def_ctor;}
    C(const C& /*other*/) noexcept {++copy_ctor; }
    C(C&& /*other*/) noexcept {++move_ctor;}

    C& operator=(const C& other) noexcept {
        if (this != &other) {
            ++copy_assign;
        }

        return *this;
    }

    C& operator=(C&& /*other*/) noexcept {
        ++move_assign;
        return *this;
    }

    ~C() {
        ++dtor;
    }

    static size_t InstanceCount() {
        return def_ctor + copy_ctor + move_ctor - dtor;
    }

    static void Reset() {
        def_ctor = 0;
        copy_ctor = 0;
        move_ctor = 0;
        copy_assign = 0;
        move_assign = 0;
        dtor = 0;
    }

    inline static size_t def_ctor = 0;
    inline static size_t copy_ctor = 0;
    inline static size_t move_ctor = 0;
    inline static size_t copy_assign = 0;
    inline static size_t move_assign = 0;
    inline static size_t dtor = 0;
};

void TestInitialization() {
    C::Reset();
    {
        Optional<C> o;
        assert(!o.HasValue());
        assert(C::InstanceCount() == 0);
    }
    assert(C::InstanceCount() == 0);

    C::Reset();
    {
        C c;
        Optional<C> o(c);
        assert(o.HasValue());
        assert(C::def_ctor == 1
               && C::copy_ctor == 1);

        assert(C::InstanceCount() == 2);
    }
    assert(C::InstanceCount() == 0);

    C::Reset();
    {
        C c;
        Optional<C> o(std::move(c));
        assert(o.HasValue());

        assert(C::def_ctor == 1
               && C::move_ctor == 1
               && C::copy_ctor == 0
               && C::copy_assign == 0
               && C::move_assign == 0);

        assert(C::InstanceCount() == 2);
    }
    assert(C::InstanceCount() == 0);

    C::Reset();
    {
        C c;
        Optional<C> o1(c);
        const Optional<C> o2(o1);
        assert(o1.HasValue());
        assert(o2.HasValue());

        assert(C::def_ctor == 1
               && C::move_ctor == 0
               && C::copy_ctor == 2
               && C::copy_assign == 0
               && C::move_assign == 0);

        assert(C::InstanceCount() == 3);
    }
    assert(C::InstanceCount() == 0);

    C::Reset();
    {
        C c;
        Optional<C> o1(c);
        const Optional<C> o2(std::move(o1));
        assert(C::def_ctor == 1
               && C::copy_ctor == 1
               && C::move_ctor == 1
               && C::copy_assign == 0
               && C::move_assign == 0);

        assert(C::InstanceCount() == 3);
    }
    assert(C::InstanceCount() == 0);
}

void TestAssignment() {
    Optional<C> o1;
    Optional<C> o2;

    {
        C::Reset();
        C c;
        o1 = c;
        assert(C::def_ctor == 1
               && C::copy_ctor == 1
               && C::dtor == 0);
    }

    {
        C::Reset();
        o2 = o1;
        assert(C::copy_ctor == 1
               && C::copy_assign == 0
               && C::dtor == 0);
    }

    {
        C::Reset();
        o2 = o1;
        assert(C::copy_ctor == 0
               && C::copy_assign == 1
               && C::dtor == 0);
    }

    {
        C::Reset();
        Optional<C> empty;
        o1 = empty;
        assert(C::copy_ctor == 0
               && C::dtor == 1);

        assert(!o1.HasValue());
    }
}

void TestMoveAssignment() {
    {
        Optional<C> o1;
        C::Reset();
        C c;
        o1 = std::move(c);
        assert(C::def_ctor == 1
               && C::move_ctor == 1
               && C::dtor == 0);
    }

    {
        Optional<C> o1;
        Optional<C> o2{C{}};
        C::Reset();
        o1 = std::move(o2);
        assert(C::move_ctor == 1
               && C::move_assign == 0
               && C::dtor == 0);
    }

    {
        Optional<C> o1{C{}};
        Optional<C> o2{C{}};
        C::Reset();
        o2 = std::move(o1);
        assert(C::copy_ctor == 0
               && C::move_assign == 1
               && C::dtor == 0);
    }

    {
        Optional<C> o1{C{}};
        C::Reset();
        Optional<C> empty;
        o1 = std::move(empty);
        assert(C::copy_ctor == 0
               && C::move_ctor == 0
               && C::move_assign == 0
               && C::dtor == 1);

        assert(!o1.HasValue());
    }
}

void TestValueAccess() {
    using namespace std::literals;

    {
        Optional<std::string> o;
        o = "hello"s;
        assert(o.HasValue());
        assert(o.Value() == "hello"s);
        assert(&*o == &o.Value());
        assert(o->length() == 5);
    }

    {
        try {
            Optional<int> o;
            [[maybe_unused]] int v = o.Value();
            assert(false);

        } catch (const BadOptionalAccess& /*e*/) {

        } catch (...) {
            assert(false);
        }
    }

}

void TestReset() {
    C::Reset();
    {
        Optional<C> o{C()};
        assert(o.HasValue());
        o.Reset();
        assert(!o.HasValue());
    }
}

void TestEmplace() {
    struct S {

        S(int i, std::unique_ptr<int>&& p) : i(i)
                                           , p(std::move(p)) {}
        int i;
        std::unique_ptr<int> p;
    };

    Optional<S> o;
    o.Emplace(1, std::make_unique<int>(2));

    assert(o.HasValue());
    assert(o->i == 1);
    assert(*(o->p) == 2);

    o.Emplace(3, std::make_unique<int>(4));

    assert(o.HasValue());
    assert(o->i == 3);
    assert(*(o->p) == 4);
}

int main() {
    try {
        TestInitialization();
        TestAssignment();
        TestMoveAssignment();
        TestValueAccess();
        TestReset();
        TestEmplace();
    } catch (...) {
        assert(false);
    }
}