optional.hpp

/*
MIT License
 
Copyright (c) 2024 mguludag
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
 
#ifndef DETAIL_OPTIONAL_HPP
#define DETAIL_OPTIONAL_HPP
 
#include "mgutility/_common/definitions.hpp"
#include "mgutility/reflection/detail/meta.hpp"
 
#include <exception>
 
#if MGUTILITY_CPLUSPLUS >= 201703L
#include <optional>
#endif
 
namespace mgutility {
 
#if MGUTILITY_CPLUSPLUS < 201703L
 
struct bad_optional_access : public std::exception {
  const char *what() const noexcept { return "optional has no value"; }
};
 
struct nullopt_t;
 
template <typename T> class optional {
public:
  MGUTILITY_CNSTXPR inline optional(nullopt_t &)
      : dummy_{0}, has_value_{false} {}
 
  MGUTILITY_CNSTXPR inline optional() : dummy_{0}, has_value_{false} {}
 
  template <typename... Args>
  MGUTILITY_CNSTXPR inline optional(Args &&...args)
      : value_{T{std::forward<Args>(args)...}}, has_value_{true} {}
 
  MGUTILITY_CNSTXPR inline optional(T &&value)
      : value_{value}, has_value_{true} {}
 
  MGUTILITY_CNSTXPR inline optional(const optional &other)
      : value_{other.value_}, has_value_{other.has_value_} {}
 
  MGUTILITY_CNSTXPR inline optional(optional &&other)
      : value_{other.value_}, has_value_{other.has_value_} {
    other.reset();
  }
 
  inline ~optional() { has_value_ = false; }
 
  MGUTILITY_CNSTXPR inline optional &operator=(const optional &other) {
    value_ = other.value_;
    has_value_ = other.has_value_;
    return *this;
  }
 
  MGUTILITY_CNSTXPR inline optional &operator=(optional &&other) {
    value_ = other.value_;
    has_value_ = other.has_value_;
    other.reset();
    return *this;
  }
 
  MGUTILITY_CNSTXPR inline void swap(optional &&other) {
    auto val = std::move(other.value_);
    other.value_ = std::move(value_);
    value_ = std::move(val);
 
    auto hval = std::move(other.has_value_);
    other.has_value_ = std::move(has_value_);
    has_value_ = std::move(hval);
  }
 
  MGUTILITY_CNSTXPR inline T &operator*() { return value_; }
 
  MGUTILITY_CNSTXPR inline T &operator*() const { return value_; }
 
  MGUTILITY_CNSTXPR inline T &value() {
    if (!has_value_)
      throw bad_optional_access();
    return value_;
  }
 
  MGUTILITY_CNSTXPR inline T &value() const {
    if (!has_value_)
      throw bad_optional_access();
    return value_;
  }
 
  MGUTILITY_CNSTXPR inline T value_or(T &&value) {
    return has_value_ ? value_ : value;
  }
 
  MGUTILITY_CNSTXPR inline T value_or(T &&value) const {
    return has_value_ ? value_ : value;
  }
 
  MGUTILITY_CNSTXPR inline T value_or(const T &value) {
    return has_value_ ? value_ : value;
  }
 
  MGUTILITY_CNSTXPR inline T value_or(const T &value) const {
    return has_value_ ? value_ : value;
  }
 
  MGUTILITY_CNSTXPR inline void emplace(T value) {
    value_ = std::move(value);
    has_value_ = true;
  }
 
  template <typename... Args>
  MGUTILITY_CNSTXPR inline void emplace(Args &&...args) {
    value_ = std::move(T{std::forward<Args>(args)...});
    has_value_ = true;
  }
 
  MGUTILITY_CNSTXPR inline bool has_value() const { return has_value_; }
 
  template <typename U = T,
            detail::enable_if_t<!std::is_destructible<U>::value, bool> = true>
  MGUTILITY_CNSTXPR inline void reset() {
    value_ = T{};
    has_value_ = false;
  }
 
  template <typename U = T,
            detail::enable_if_t<std::is_destructible<T>::value, bool> = true>
  MGUTILITY_CNSTXPR inline void reset() {
    value_.~T();
    has_value_ = false;
  }
 
  MGUTILITY_CNSTXPR operator bool() { return has_value_; }
 
private:
  union {
    T value_;
    char dummy_[sizeof(T)];
  };
  bool has_value_;
};
 
struct nullopt_t {
  template <typename T> MGUTILITY_CNSTXPR operator optional<T>() {
    return optional<T>{};
  }
};
 
auto nullopt = nullopt_t{};
 
#else
template <typename T> using optional = std::optional<T>;
 
inline constexpr auto nullopt{std::nullopt};
 
#endif
} // namespace mgutility
 
#endif // DETAIL_OPTIONAL_HPP