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// This file is part of OpenCV project.
// It is subject to the license terms in the LICENSE file found in the top-level directory
// of this distribution and at http://opencv.org/license.html.
//
// Copyright (C) 2018 Intel Corporation
#ifndef OPENCV_GAPI_UTIL_OPTIONAL_HPP
#define OPENCV_GAPI_UTIL_OPTIONAL_HPP
#include <opencv2/gapi/util/variant.hpp>
// A poor man's `optional` implementation, incompletely modeled against C++17 spec.
namespace cv
{
namespace util
{
class bad_optional_access: public std::exception
{
public:
virtual const char *what() const noexcept override
{
return "Bad optional access";
}
};
// TODO: nullopt_t
// Interface ///////////////////////////////////////////////////////////////
template<typename T> class optional
{
public:
// Constructors
// NB.: there were issues with Clang 3.8 when =default() was used
// instead {}
optional() {}
optional(const optional&) = default;
explicit optional(T&&) noexcept;
explicit optional(const T&) noexcept;
optional(optional&&) noexcept;
// TODO: optional(nullopt_t) noexcept;
// TODO: optional(const optional<U> &)
// TODO: optional(optional<U> &&)
// TODO: optional(Args&&...)
// TODO: optional(initializer_list<U>)
// TODO: optional(U&& value);
// Assignment
optional& operator=(const optional&) = default;
optional& operator=(optional&&);
// Observers
T* operator-> ();
const T* operator-> () const;
T& operator* ();
const T& operator* () const;
// TODO: && versions
operator bool() const noexcept;
bool has_value() const noexcept;
T& value();
const T& value() const;
// TODO: && versions
template<class U>
T value_or(U &&default_value) const;
void swap(optional &other) noexcept;
void reset() noexcept;
// TODO: emplace
// TODO: operator==, !=, <, <=, >, >=
private:
struct nothing {};
util::variant<nothing, T> m_holder;
};
template<class T>
optional<typename std::decay<T>::type> make_optional(T&& value);
// TODO: Args... and initializer_list versions
// Implementation //////////////////////////////////////////////////////////
template<class T> optional<T>::optional(T &&v) noexcept
: m_holder(std::move(v))
{
}
template<class T> optional<T>::optional(const T &v) noexcept
: m_holder(v)
{
}
template<class T> optional<T>::optional(optional&& rhs) noexcept
: m_holder(std::move(rhs.m_holder))
{
rhs.reset();
}
template<class T> optional<T>& optional<T>::operator=(optional&& rhs)
{
m_holder = std::move(rhs.m_holder);
rhs.reset();
return *this;
}
template<class T> T* optional<T>::operator-> ()
{
return & *(*this);
}
template<class T> const T* optional<T>::operator-> () const
{
return & *(*this);
}
template<class T> T& optional<T>::operator* ()
{
return this->value();
}
template<class T> const T& optional<T>::operator* () const
{
return this->value();
}
template<class T> optional<T>::operator bool() const noexcept
{
return this->has_value();
}
template<class T> bool optional<T>::has_value() const noexcept
{
return util::holds_alternative<T>(m_holder);
}
template<class T> T& optional<T>::value()
{
if (!this->has_value())
throw_error(bad_optional_access());
return util::get<T>(m_holder);
}
template<class T> const T& optional<T>::value() const
{
if (!this->has_value())
throw_error(bad_optional_access());
return util::get<T>(m_holder);
}
template<class T>
template<class U> T optional<T>::value_or(U &&default_value) const
{
return (this->has_value() ? this->value() : T(default_value));
}
template<class T> void optional<T>::swap(optional<T> &other) noexcept
{
m_holder.swap(other.m_holder);
}
template<class T> void optional<T>::reset() noexcept
{
if (this->has_value())
m_holder = nothing{};
}
template<class T>
optional<typename std::decay<T>::type> make_optional(T&& value)
{
return optional<typename std::decay<T>::type>(std::forward<T>(value));
}
} // namespace util
} // namespace cv
#endif // OPENCV_GAPI_UTIL_OPTIONAL_HPP
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