unset.h

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2025 Alex2772 and Contributors
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
//
// Created by alex2 on 03.01.2021.
//
 
#pragma once
 
#include <AUI/Traits/concepts.h>
#include <AUI/Util/Assert.h>
#include <algorithm>
#include <ostream>
 
#include <fmt/core.h>
 
namespace ass {
 
   template<typename T>
   struct unset_wrap {
   private:
       T stored;
       bool set = false;
 
   public:
       unset_wrap() noexcept
       {
       }
 
       template<typename V>
       unset_wrap(const V& v);
 
       template<typename V>
       unset_wrap(V&& v);
 
       T& operator*() {
           AUI_ASSERT(bool(*this));
           return stored;
       }
       const T& operator*() const {
           AUI_ASSERT(bool(*this));
           return stored;
       }
       T* operator->() {
           AUI_ASSERT(bool(*this));
           return &stored;
       }
       const T* operator->() const {
           AUI_ASSERT(bool(*this));
           return &stored;
       }
       T orDefault(const T& def) const {
           if (set) {
               return stored;
           }
           return def;
       }
 
       template<typename Destination>
       void bindTo(Destination& destination) const {
           if (set) {
               destination = stored;
           }
       }
 
       unset_wrap<T>& operator=(const unset_wrap<T>& v) noexcept;
 
       template<aui::convertible_to<T> U>
       unset_wrap<T>& operator=(const unset_wrap<U>& v) noexcept;
 
       bool operator==(const unset_wrap<T>& other) const {
           if (set != other.set) {
               return false;
           }
           if (set) {
               return stored == other.stored;
           }
           return true;
       }
       bool operator!=(const unset_wrap<T>& other) const {
           return !(*this == other);
       }
 
       void reset() noexcept {
           set = false;
       }
 
       operator bool() const {
           return set;
       }
 
       struct unset_wrap_tag {};
   };
 
   namespace detail::unset {
       template<typename T, aui::convertible_to<T> U>
       void init(unset_wrap<T>& wrap, T& dst, bool& set, const unset_wrap<U>& value) {
           if (value) {
               dst = static_cast<T>(*value);
               set = true;
           }
       }
       template<typename T, aui::convertible_to<T> U>
       void init(unset_wrap<T>& wrap, T& dst, bool& set, unset_wrap<U>&& value) {
           if (value) {
               dst = static_cast<T&&>(*value);
               set = true;
           }
       }
       template<typename T, aui::convertible_to<T> U>
       void init(unset_wrap<T>& wrap, T& dst, bool& set, U&& value) {
           dst = static_cast<T&&>(value);
           set = true;
       }
       template<typename T, aui::convertible_to<T> U>
       void init(unset_wrap<T>& wrap, T& dst, bool& set, const U& value) {
           dst = static_cast<T>(value);
           set = true;
       }
   }
 
 
   template<typename T>
   template<typename V>
   unset_wrap<T>::unset_wrap(const V& v)
   {
       detail::unset::init(*this, stored, set, v);
   }
 
 
   template<typename T>
   template<typename V>
   unset_wrap<T>::unset_wrap(V&& v)
   {
       detail::unset::init(*this, stored, set, std::forward<V>(v));
   }
 
   template<typename T>
   unset_wrap<T>& unset_wrap<T>::operator=(const unset_wrap<T>& v) noexcept {
       detail::unset::init(*this, stored, set, v);
       return *this;
   }
 
   template<typename T>
   template<aui::convertible_to<T> U>
   unset_wrap<T>& unset_wrap<T>::operator=(const unset_wrap<U>& v) noexcept {
       detail::unset::init(*this, stored, set, v);
       return *this;
   }
 
}
 
template <typename T> struct fmt::formatter<ass::unset_wrap<T>> {
   template<typename ParseContext>
   constexpr auto parse(ParseContext& ctx)
   {
       return ctx.begin();
   }
 
   auto format(ass::unset_wrap<T> c, format_context& ctx) const {
       if (c) {
           return fmt::format_to(ctx.out(), "{}", *c);
       } else {
           return fmt::format_to(ctx.out(), "<unset>");
       }
   }
};
 
template<typename T>
std::ostream& operator<<(std::ostream& o, const ass::unset_wrap<T>& wrap) {
   if (wrap) {
       o << *wrap;
   } else {
       o << "<unset>";
   }
   return o;
}

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