2021-05-31 22:26:44 +02:00
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/*
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* This file is part of OpenTTD.
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* OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
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* OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
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*/
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/** @file span_type.hpp Minimized implementation of C++20 std::span. */
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#ifndef CORE_SPAN_TYPE_HPP
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#define CORE_SPAN_TYPE_HPP
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/* This is a partial copy/paste from https://github.com/gsl-lite/gsl-lite/blob/master/include/gsl/gsl-lite.hpp */
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/* Template to check if a template variable defines size() and data(). */
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template <class, class = void>
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struct has_size_and_data : std::false_type{};
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template <class C>
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struct has_size_and_data
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<
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C, std::void_t<
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decltype(std::size(std::declval<C>())),
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decltype(std::data(std::declval<C>()))>
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> : std::true_type{};
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/* Template to check if two elements are compatible. */
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template <class, class, class = void>
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struct is_compatible_element : std::false_type {};
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template <class C, class E>
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struct is_compatible_element
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<
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C, E, std::void_t<
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decltype(std::data(std::declval<C>())),
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2021-10-28 23:10:03 +02:00
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typename std::remove_pointer_t<decltype(std::data( std::declval<C&>()))>(*)[]>
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> : std::is_convertible<typename std::remove_pointer_t<decltype(std::data(std::declval<C&>()))>(*)[], E(*)[]>{};
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2021-05-31 22:26:44 +02:00
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/* Template to check if a container is compatible. gsl-lite also includes is_array and is_std_array, but as we don't use them, they are omitted. */
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template <class C, class E>
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struct is_compatible_container : std::bool_constant
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<
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has_size_and_data<C>::value
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&& is_compatible_element<C,E>::value
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>{};
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/**
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* A trimmed down version of what std::span will be in C++20.
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*
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* It is fully forwards compatible, so if this codebase switches to C++20,
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* all "span" instances can be replaced by "std::span" without loss of
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* functionality.
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*
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* Currently it only supports basic functionality:
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* - size() and friends
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* - begin() and friends
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*
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* It is meant to simplify function parameters, where we only want to walk
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* a continuous list.
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*/
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template<class T>
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class span {
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public:
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typedef T element_type;
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typedef typename std::remove_cv< T >::type value_type;
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typedef T &reference;
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typedef T *pointer;
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typedef const T &const_reference;
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typedef const T *const_pointer;
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typedef pointer iterator;
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typedef const_pointer const_iterator;
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typedef size_t size_type;
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typedef std::ptrdiff_t difference_type;
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2021-06-14 10:05:30 +02:00
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constexpr span() noexcept : first(nullptr), last(nullptr) {}
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2021-05-31 22:26:44 +02:00
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constexpr span(pointer data_in, size_t size_in) : first(data_in), last(data_in + size_in) {}
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template<class Container, typename std::enable_if<(is_compatible_container<Container, element_type>::value), int>::type = 0>
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constexpr span(Container &list) noexcept : first(std::data(list)), last(std::data(list) + std::size(list)) {}
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template<class Container, typename std::enable_if<(std::is_const<element_type>::value && is_compatible_container<Container, element_type>::value), int>::type = 0>
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constexpr span(const Container &list) noexcept : first(std::data(list)), last(std::data(list) + std::size(list)) {}
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constexpr size_t size() const noexcept { return static_cast<size_t>( last - first ); }
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constexpr std::ptrdiff_t ssize() const noexcept { return static_cast<std::ptrdiff_t>( last - first ); }
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constexpr bool empty() const noexcept { return size() == 0; }
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constexpr iterator begin() const noexcept { return iterator(first); }
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constexpr iterator end() const noexcept { return iterator(last); }
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constexpr const_iterator cbegin() const noexcept { return const_iterator(first); }
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constexpr const_iterator cend() const noexcept { return const_iterator(last); }
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2021-10-28 23:48:26 +02:00
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constexpr reference operator[](size_type idx) const { return first[idx]; }
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2021-05-31 22:26:44 +02:00
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private:
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pointer first;
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pointer last;
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};
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#endif /* CORE_SPAN_TYPE_HPP */
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