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issue-template

aka_constexpr_map.hh
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			#include <array>
			#include <tuple>
			#include <type_traits>

			#ifndef AKANTU_CONSTEXPR_MAP_HH
			#define AKANTU_CONSTEXPR_MAP_HH

			namespace akantu {
			namespace details {
			template <class InputIt, class UnaryPredicate>
			constexpr InputIt my_find_if(InputIt first, InputIt last,
			UnaryPredicate && p) {
			for (; first != last; ++first) {
			if (std::forward<UnaryPredicate>(p)(*first)) {
			return first;
			}
			}
			return last;
			}

			// Author Jason Turner C++ Weekly ep 233
			template <typename Key, typename Value, std::size_t Size>
			struct ConstexprMap {
			std::array<std::pair<Key, Value>, Size> data;

			[[nodiscard]] constexpr Value at(const Key & key) const {
			const auto it =
			my_find_if(data.begin(), data.end(),
			[&key](const auto & val) { return val.first == key; });

			if (it != data.end()) {
			return it->second;
			} else {
			throw std::range_error("Key out of range");
			}
			}

			[[nodiscard]] constexpr auto find(const Key & key) const {
			const auto it =
			my_find_if(data.begin(), data.end(),
			[&key](const auto & val) { return val.first == key; });

			return it;
			}

			[[nodiscard]] constexpr auto begin() const { return data.begin(); }
			[[nodiscard]] constexpr auto end() const { return data.end(); }
			};

			// magic_switch from
			// https://stackoverflow.com/questions/39915986/solutions-for-dynamic-dispatch-on-unrelated-types
			template <class Function, class DynamicType, class Tuple,
			class DefaultFunction, std::size_t... Is>
			[[gnu::visibility("hidden")]] constexpr decltype(auto) static_switch_dispatch(
			const Tuple &, Function && function, const DynamicType & type,
			DefaultFunction && default_function, std::index_sequence<Is...> /is/) {
			auto * function_pointer = std::addressof(function);
			using FunctionPointer = decltype(function_pointer);
			using Ret = decltype(function(std::tuple_element_t<0, Tuple>{}));
			using TableEntry = Ret (*)(FunctionPointer);

			constexpr std::array<std::pair<DynamicType, std::size_t>, sizeof...(Is)>
			data{{{std::tuple_element_t<Is, Tuple>::value, Is}...}};

			constexpr auto map =
			ConstexprMap<DynamicType, std::size_t, data.size()>{{data}};

			constexpr TableEntry table[] = {
			[](FunctionPointer function_pointer) -> Ret {
			return (*function_pointer)(std::tuple_element_t<Is, Tuple>{});
			}...};

			auto it = map.find(type);
			if (it != map.end()) {
			return table[it->second](function_pointer);
			} else {
			return default_function(type);
			}
			}
			} // namespace details
			} // namespace akantu

			#endif // AKANTU_CONSTEXPR_MAP_HH

rAKA/src/common/aka_constexpr_map.hh08fb99482f17features/issue-template

aka_constexpr_map.hhView Options

rAKA/src/common/aka_constexpr_map.hh
08fb99482f17features/issue-template

aka_constexpr_map.hh
View Options