forked from OctaForge/libostd
allow constructing unordered_maps from any 2-tuple range
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407d4a524f
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@ -33,6 +33,19 @@ struct ranged_traits<std::unordered_map<K, T, H, E, A> const> {
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}
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};
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namespace detail {
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template<typename T>
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std::integral_constant<
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bool, std::tuple_size<T>::value == 2
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> tuple2_like_test(typename std::tuple_size<T>::type *);
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template<typename>
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std::false_type tuple2_like_test(...);
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template<typename T>
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constexpr bool is_2tuple_like = decltype(tuple2_like_test<T>(0))::value;
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}
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template<
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typename K, typename T, typename H = std::hash<K>,
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typename E = std::equal_to<K>,
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@ -42,14 +55,39 @@ inline std::unordered_map<K, T, H, E, A> make_unordered_map(
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R range, size_t bcount = 1, H const &hash = H{},
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E const &kequal = E{}, A const &alloc = A{}
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) {
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static_assert(
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detail::is_2tuple_like<RangeValue<R>>,
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"the range element must be a pair/2-tuple"
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);
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using MP = std::pair<K const, T>;
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using AK = std::tuple_element_t<0, RangeValue<R>>;
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using AV = std::tuple_element_t<1, RangeValue<R>>;
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static_assert(
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std::is_constructible_v<K const, AK> && std::is_constructible_v<T, AV>,
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"incompatible range element type"
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);
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std::unordered_map<K, T, H, E, A> ret{bcount, hash, kequal, alloc};
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using C = RangeCategory<R>;
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if constexpr(std::is_convertible_v<C, FiniteRandomAccessRangeTag>) {
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/* at least try to preallocate here... */
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ret.reserve(range.size());
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}
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for (; !range.empty(); range.pop_front()) {
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if constexpr(std::is_constructible_v<MP, RangeValue<R>>) {
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ret.emplace(range.front());
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} else {
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/* store a temporary to prevent calling front() twice; however,
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* for values that can be used to construct the pair directly
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* we can just do the above
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*/
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RangeValue<R> v{range.front()};
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ret.emplace(std::move(std::get<0>(v)), std::move(std::get<1>(v)));
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}
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}
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return ret;
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}
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@ -59,19 +97,24 @@ template<
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typename H = std::hash<typename RangeValue<R>::first_type>,
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typename E = std::equal_to<typename RangeValue<R>::first_type>,
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typename A = std::allocator<std::pair<
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typename RangeValue<R>::first_type, typename RangeValue<R>::second_type
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std::tuple_element_t<0, RangeValue<R>>,
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std::tuple_element_t<1, RangeValue<R>>
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>>
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>
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inline std::unordered_map<
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typename RangeValue<R>::first_type,
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typename RangeValue<R>::second_type, H, E, A
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std::tuple_element_t<0, RangeValue<R>>,
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std::tuple_element_t<1, RangeValue<R>>, H, E, A
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> make_unordered_map(
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R &&range, size_t bcount = 1, H const &hash = H{},
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E const &kequal = E{}, A const &alloc = A{}
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) {
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static_assert(
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detail::is_2tuple_like<RangeValue<R>>,
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"the range elements must be pairs/2-tuples"
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);
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return make_unordered_map<
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typename RangeValue<R>::first_type,
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typename RangeValue<R>::second_type, H, E, A
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std::tuple_element_t<0, RangeValue<R>>,
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std::tuple_element_t<1, RangeValue<R>>, H, E, A
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>(std::forward<R>(range), bcount, hash, kequal, alloc);
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}
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