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// Copyright © 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
// 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024
// Vladimír Vondruš <mosra@centrum.cz> and contributors
// Copyright © 2020-2024 Dan R.
//
// 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.
#pragma once
#include <type_traits>
namespace Death { namespace Containers {
//###==##====#=====--==~--~=~- --- -- - - - -
namespace Implementation
{
template<class, class> struct ReferenceConverter;
}
/**
@brief Lightweight non-owning reference wrapper
Equivalent to @ref std::reference_wrapper from C++11, provides a copyable non-owning wrapper over
l-value references to allow storing them in containers. Unlike @ref std::reference_wrapper, this class
does not provide @cpp operator() @ce and there are no equivalents to @ref std::ref() / @ref std::cref()
as they are not deemed necessary --- in most contexts where @ref Reference is used, passing a plain reference
works just as well. This class is trivially copyable (@ref std::reference_wrapper is guaranteed to be so
only since C++17) and also works on incomplete types, which @ref std::reference_wrapper knows since C++20.
This class is exclusively for l-value references.
*/
template<class T> class Reference
{
public:
/** @brief Constructor */
constexpr /*implicit*/ Reference(T& reference) noexcept : _reference{&reference} {}
/**
* @brief Construct a reference from external representation
*/
template<class U, class = decltype(Implementation::ReferenceConverter<T, U>::from(std::declval<U>()))> constexpr /*implicit*/ Reference(U other) noexcept : Reference{Implementation::ReferenceConverter<T, U>::from(other)} { }
/**
* @brief Construction from r-value references is not allowed
*/
Reference(T&&) = delete;
/**
* @brief Construct a reference from another of a derived type
*
* Expects that @p T is a base of @p U.
*/
template<class U
#ifndef DOXYGEN_GENERATING_OUTPUT
, typename std::enable_if<std::is_base_of<T, U>::value, int>::type = 0
#endif
> constexpr /*implicit*/ Reference(Reference<U> other) noexcept : _reference{other._reference} { }
/**
* @brief Convert the reference to external representation
*/
template<class U, class = decltype(Implementation::ReferenceConverter<T, U>::to(std::declval<Reference<T>>()))> constexpr /*implicit*/ operator U() const
{
return Implementation::ReferenceConverter<T, U>::to(*this);
}
/** @brief Underlying reference */
constexpr /*implicit*/ operator T& () const
{
return *_reference;
}
/** @overload */
constexpr /*implicit*/ operator Reference<const T>() const
{
return *_reference;
}
/** @brief Underlying reference */
constexpr T& get() const
{
return *_reference;
}
/**
* @brief Access the underlying reference
*/
constexpr T* operator->() const
{
return _reference;
}
/**
* @brief Access the underlying reference
*/
constexpr T& operator*() const
{
return *_reference;
}
private:
// For the conversion constructor
template<class U> friend class Reference;
T* _reference;
};
/** @relatesalso Reference
@brief Make a reference wrapper
Convenience alternative to @ref Reference::Reference(T&).
Useful for example when iterating a list of variables that need to be modified
in-place, and where the code would otherwise have to be extra verbose or would
fall back to raw pointers and risk them getting @cpp nullptr @ce.
*/
template<class T> constexpr Reference<T> reference(T& reference) {
return Reference<T>{reference};
}
}}
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