optional.h

#pragma once
#include <cstddef>
#include <cassert>
#include <utility>
#include <cstdint>
 
namespace smlt {
 
/* When all compilers support the true optional class we can delete this. This exists largely for compatibility
 * with old GCC for the Dreamcast port */
 
template<typename T>
class optional {
public:
    optional() = default;
 
    ~optional() {
        reset();
    }
 
    template<typename U>
    optional(optional<U>&& other) {
        auto src = other.value_ptr();
        if(src) {
            set_value(std::move(*src));
        } else {
            reset();
        }
    }
 
    optional(const T& value) {
        set_value(value);
    }
 
    optional(T&& value) {
        set_value(std::move(value));
    }
 
    optional(const optional<T>& rhs) {
        if(rhs.has_value()) {
            set_value(rhs.value());
        }
    }
 
    optional& operator=(const optional& other) {
        if(other.has_value()) {
            set_value(other.value());
        } else {
            reset();
        }
 
        return *this;
    }
 
    explicit operator bool() const {
        return has_value();
    }
 
    bool has_value() const { return has_value_; }
 
    const T& value() const {
        assert(has_value());
        return *value_ptr();
    }
 
    T& value() {
        assert(has_value());
        return *value_ptr();
    }
 
    T value_or(T&& def) const {
        bool(*this) ? **this : static_cast<T>(std::forward<T>(def));
    }
 
    T value_or(T&& def) {
        return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<T>(def));
    }
 
    const T* operator->() const {
        assert(has_value());
        return value_ptr();
    }
 
    T* operator->() {
        assert(has_value());
        return value_ptr();
    }
 
    const T& operator*() const {
        assert(has_value());
        return *value_ptr();
    }
 
    T& operator*() {
        assert(has_value());
        return *value_ptr();
    }
 
private:
    uint8_t data_[sizeof(T)] __attribute__((aligned(8)));
    bool has_value_ = false;
 
    T* value_ptr() const {
        return (has_value()) ? (T*) (data_) : nullptr;
    }
 
    void set_value(const T& value) {
        if(has_value()) {
            reset();
        }
 
        new (data_) T();
        has_value_ = true;
        *(value_ptr()) = value;
    }
 
    void set_value(T&& value) {
        if(has_value()) {
            // We destroy the current value if we have one
            reset();
        }
 
        new (data_) T(std::move(value));
        has_value_ = true;
    }
 
    void reset() {
        T* v = value_ptr();
        if(v) {
            has_value_ = false;
            v->~T();
        }
    }
};
 
 
}