// This file is part of OpenCV project.
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// It is subject to the license terms in the LICENSE file found in the top-level directory
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// of this distribution and at http://opencv.org/license.html.
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//
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// Copyright (C) 2018 Intel Corporation
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#ifndef OPENCV_GAPI_UTIL_VARIANT_HPP
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#define OPENCV_GAPI_UTIL_VARIANT_HPP
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#include <array>
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#include <type_traits>
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#include <opencv2/gapi/util/throw.hpp>
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#include <opencv2/gapi/util/util.hpp> // max_of_t
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// A poor man's `variant` implementation, incompletely modeled against C++17 spec.
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namespace cv
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{
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namespace util
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{
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namespace detail
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{
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template<std::size_t I, typename Target, typename First, typename... Remaining>
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struct type_list_index_helper
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{
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static const constexpr bool is_same = std::is_same<Target, First>::value;
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static const constexpr std::size_t value =
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std::conditional<is_same, std::integral_constant<std::size_t, I>, type_list_index_helper<I + 1, Target, Remaining...>>::type::value;
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};
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template<std::size_t I, typename Target, typename First>
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struct type_list_index_helper<I, Target, First>
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{
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static_assert(std::is_same<Target, First>::value, "Type not found");
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static const constexpr std::size_t value = I;
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};
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template<class T, class U, class V> using are_different =
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std::enable_if<!std::is_same<typename std::decay<T>::type,
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typename std::decay<U>::type>::value,
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V>;
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}
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template<typename Target, typename... Types>
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struct type_list_index
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{
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static const constexpr std::size_t value = detail::type_list_index_helper<0, Target, Types...>::value;
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};
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class bad_variant_access: public std::exception
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{
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public:
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virtual const char *what() const noexcept override
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{
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return "Bad variant access";
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}
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};
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// Interface ///////////////////////////////////////////////////////////////
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struct monostate {};
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inline bool operator==(const util::monostate&, const util::monostate&)
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{
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return true;
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}
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template<typename... Ts> // FIXME: no references, arrays, and void
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class variant
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{
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// FIXME: Replace with std::aligned_union after gcc4.8 support is dropped
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static constexpr const std::size_t S = cv::detail::max_of_t<sizeof(Ts)...>::value;
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static constexpr const std::size_t A = cv::detail::max_of_t<alignof(Ts)...>::value;
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using Memory = typename std::aligned_storage<S, A>::type[1];
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template<typename T> struct cctr_h {
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static void help(Memory memory, const Memory from) {
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new (memory) T(*reinterpret_cast<const T*>(from));
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}
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};
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template<typename T> struct vctr_h {
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static void help(Memory memory, const void* pval) {
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new (memory) T(*reinterpret_cast<const T*>(pval));
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}
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};
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template<typename T> struct mctr_h {
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static void help(Memory memory, void *pval) {
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new (memory) T(std::move(*reinterpret_cast<T*>(pval)));
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}
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};
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template<typename T> struct copy_h {
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static void help(Memory to, const Memory from) {
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*reinterpret_cast<T*>(to) = *reinterpret_cast<const T*>(from);
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}
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};
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template<typename T> struct move_h {
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static void help(Memory to, const Memory from) {
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*reinterpret_cast<T*>(to) = std::move(*reinterpret_cast<const T*>(from));
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}
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};
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template<typename T> struct swap_h {
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static void help(Memory to, Memory from) {
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std::swap(*reinterpret_cast<T*>(to), *reinterpret_cast<T*>(from));
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}
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};
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template<typename T> struct dtor_h {
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static void help(Memory memory) {
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(void) memory; // MSCV warning
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reinterpret_cast<T*>(memory)->~T();
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}
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};
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template<typename T> struct equal_h {
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static bool help(const Memory lhs, const Memory rhs) {
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const T& t_lhs = *reinterpret_cast<const T*>(lhs);
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const T& t_rhs = *reinterpret_cast<const T*>(rhs);
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return t_lhs == t_rhs;
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}
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};
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typedef void (*CCtr) (Memory, const Memory); // Copy c-tor (variant)
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typedef void (*VCtr) (Memory, const void*); // Copy c-tor (value)
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typedef void (*MCtr) (Memory, void*); // Generic move c-tor
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typedef void (*Copy) (Memory, const Memory); // Copy assignment
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typedef void (*Move) (Memory, const Memory); // Move assignment
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typedef void (*Swap) (Memory, Memory); // Swap
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typedef void (*Dtor) (Memory); // Destructor
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typedef bool (*Equal)(const Memory, const Memory); // Equality test (external)
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static constexpr std::array<CCtr, sizeof...(Ts)> cctrs(){ return {{(&cctr_h<Ts>::help)...}};}
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static constexpr std::array<VCtr, sizeof...(Ts)> vctrs(){ return {{(&vctr_h<Ts>::help)...}};}
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static constexpr std::array<MCtr, sizeof...(Ts)> mctrs(){ return {{(&mctr_h<Ts>::help)...}};}
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static constexpr std::array<Copy, sizeof...(Ts)> cpyrs(){ return {{(©_h<Ts>::help)...}};}
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static constexpr std::array<Move, sizeof...(Ts)> mvers(){ return {{(&move_h<Ts>::help)...}};}
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static constexpr std::array<Swap, sizeof...(Ts)> swprs(){ return {{(&swap_h<Ts>::help)...}};}
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static constexpr std::array<Dtor, sizeof...(Ts)> dtors(){ return {{(&dtor_h<Ts>::help)...}};}
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std::size_t m_index = 0;
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protected:
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template<typename T, typename... Us> friend T& get(variant<Us...> &v);
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template<typename T, typename... Us> friend const T& get(const variant<Us...> &v);
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template<typename... Us> friend bool operator==(const variant<Us...> &lhs,
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const variant<Us...> &rhs);
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Memory memory;
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public:
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// Constructors
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variant() noexcept;
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variant(const variant& other);
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variant(variant&& other) noexcept;
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template<typename T> explicit variant(const T& t);
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// are_different is a SFINAE trick to avoid variant(T &&t) with T=variant
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// for some reason, this version is called instead of variant(variant&& o) when
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// variant is used in STL containers (examples: vector assignment)
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template<typename T> explicit variant(T&& t, typename detail::are_different<variant, T, int>::type = 0);
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// template<class T, class... Args> explicit variant(Args&&... args);
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// FIXME: other constructors
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// Destructor
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~variant();
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// Assignment
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variant& operator=(const variant& rhs);
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variant& operator=(variant &&rhs) noexcept;
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// SFINAE trick to avoid operator=(T&&) with T=variant<>, see comment above
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template<class T>
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typename detail::are_different<variant, T, variant&>
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::type operator=(T&& t) noexcept;
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// Observers
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std::size_t index() const noexcept;
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// FIXME: valueless_by_exception()
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// Modifiers
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// FIXME: emplace()
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void swap(variant &rhs) noexcept;
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// Non-C++17x!
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template<typename T> static constexpr std::size_t index_of();
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};
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// FIMXE: visit
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template<typename T, typename... Types>
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T& get(util::variant<Types...> &v);
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template<typename T, typename... Types>
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const T& get(const util::variant<Types...> &v);
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template<typename T, typename... Types>
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bool holds_alternative(const util::variant<Types...> &v) noexcept;
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// FIXME: T&&, const TT&& versions.
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// Implementation //////////////////////////////////////////////////////////
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template<typename... Ts>
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variant<Ts...>::variant() noexcept
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{
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typedef typename std::tuple_element<0, std::tuple<Ts...> >::type TFirst;
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new (memory) TFirst();
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}
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template<typename... Ts>
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variant<Ts...>::variant(const variant &other)
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: m_index(other.m_index)
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{
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(cctrs()[m_index])(memory, other.memory);
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}
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template<typename... Ts>
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variant<Ts...>::variant(variant &&other) noexcept
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: m_index(other.m_index)
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{
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(mctrs()[m_index])(memory, other.memory);
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}
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template<typename... Ts>
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template<class T>
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variant<Ts...>::variant(const T& t)
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: m_index(util::type_list_index<T, Ts...>::value)
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{
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(vctrs()[m_index])(memory, &t);
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}
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template<typename... Ts>
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template<class T>
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variant<Ts...>::variant(T&& t, typename detail::are_different<variant, T, int>::type)
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: m_index(util::type_list_index<typename std::remove_reference<T>::type, Ts...>::value)
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{
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(mctrs()[m_index])(memory, &t);
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}
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template<typename... Ts>
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variant<Ts...>::~variant()
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{
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(dtors()[m_index])(memory);
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}
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template<typename... Ts>
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variant<Ts...>& variant<Ts...>::operator=(const variant<Ts...> &rhs)
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{
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if (m_index != rhs.m_index)
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{
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(dtors()[ m_index])(memory);
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(cctrs()[rhs.m_index])(memory, rhs.memory);
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m_index = rhs.m_index;
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}
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else
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{
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(cpyrs()[rhs.m_index])(memory, rhs.memory);
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}
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return *this;
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}
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template<typename... Ts>
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variant<Ts...>& variant<Ts...>::operator=(variant<Ts...> &&rhs) noexcept
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{
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if (m_index != rhs.m_index)
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{
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(dtors()[ m_index])(memory);
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(mctrs()[rhs.m_index])(memory, rhs.memory);
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m_index = rhs.m_index;
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}
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else
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{
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(mvers()[rhs.m_index])(memory, rhs.memory);
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}
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return *this;
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}
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template<typename... Ts>
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template<class T> typename detail::are_different<variant<Ts...>, T, variant<Ts...>&>
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::type variant<Ts...>::operator=(T&& t) noexcept
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{
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// FIXME: No version with implicit type conversion available!
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static const constexpr std::size_t t_index =
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util::type_list_index<T, Ts...>::value;
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if (t_index == m_index)
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{
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util::get<T>(*this) = std::move(t);
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return *this;
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}
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else return (*this = variant(std::move(t)));
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}
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template<typename... Ts>
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std::size_t util::variant<Ts...>::index() const noexcept
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{
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return m_index;
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}
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template<typename... Ts>
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void variant<Ts...>::swap(variant<Ts...> &rhs) noexcept
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{
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if (m_index == rhs.index())
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{
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(swprs()[m_index](memory, rhs.memory));
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}
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else
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{
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variant<Ts...> tmp(std::move(*this));
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*this = std::move(rhs);
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rhs = std::move(tmp);
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}
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}
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template<typename... Ts>
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template<typename T>
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constexpr std::size_t variant<Ts...>::index_of()
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{
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return util::type_list_index<T, Ts...>::value; // FIXME: tests!
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}
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template<typename T, typename... Types>
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T& get(util::variant<Types...> &v)
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{
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const constexpr std::size_t t_index =
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util::type_list_index<T, Types...>::value;
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if (v.index() == t_index)
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return *(T*)(&v.memory); // workaround for ICC 2019
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// original code: return reinterpret_cast<T&>(v.memory);
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else
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throw_error(bad_variant_access());
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}
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template<typename T, typename... Types>
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const T& get(const util::variant<Types...> &v)
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{
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const constexpr std::size_t t_index =
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util::type_list_index<T, Types...>::value;
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if (v.index() == t_index)
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return *(const T*)(&v.memory); // workaround for ICC 2019
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// original code: return reinterpret_cast<const T&>(v.memory);
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else
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throw_error(bad_variant_access());
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}
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template<typename T, typename... Types>
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bool holds_alternative(const util::variant<Types...> &v) noexcept
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{
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return v.index() == util::variant<Types...>::template index_of<T>();
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}
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template<typename... Us> bool operator==(const variant<Us...> &lhs,
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const variant<Us...> &rhs)
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{
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using V = variant<Us...>;
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// Instantiate table only here since it requires operator== for <Us...>
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// <Us...> should have operator== only if this one is used, not in general
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static const std::array<typename V::Equal, sizeof...(Us)> eqs = {
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{(&V::template equal_h<Us>::help)...}
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};
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if (lhs.index() != rhs.index())
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return false;
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return (eqs[lhs.index()])(lhs.memory, rhs.memory);
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}
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template<typename... Us> bool operator!=(const variant<Us...> &lhs,
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const variant<Us...> &rhs)
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{
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return !(lhs == rhs);
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}
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} // namespace cv
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} // namespace util
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#endif // OPENCV_GAPI_UTIL_VARIANT_HPP
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