300 lines
7.3 KiB
C++
300 lines
7.3 KiB
C++
// Boost.Geometry
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// Copyright (c) 2020-2021, Oracle and/or its affiliates.
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// Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
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// Licensed under the Boost Software License version 1.0.
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// http://www.boost.org/users/license.html
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#ifndef BOOST_GEOMETRY_UTIL_SEQUENCE_HPP
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#define BOOST_GEOMETRY_UTIL_SEQUENCE_HPP
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#include <type_traits>
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namespace boost { namespace geometry
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{
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namespace util
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{
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// An alternative would be to use std:tuple and std::pair
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// but it would add dependency.
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template <typename ...Ts>
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struct type_sequence {};
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// true if T is a sequence
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template <typename T>
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struct is_sequence : std::false_type {};
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template <typename ...Ts>
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struct is_sequence<type_sequence<Ts...>> : std::true_type {};
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template <typename T, T ...Is>
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struct is_sequence<std::integer_sequence<T, Is...>> : std::true_type {};
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// number of elements in a sequence
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template <typename Sequence>
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struct sequence_size {};
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template <typename ...Ts>
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struct sequence_size<type_sequence<Ts...>>
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: std::integral_constant<std::size_t, sizeof...(Ts)>
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{};
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template <typename T, T ...Is>
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struct sequence_size<std::integer_sequence<T, Is...>>
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: std::integral_constant<std::size_t, sizeof...(Is)>
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{};
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// element of a sequence
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template <std::size_t I, typename Sequence>
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struct sequence_element {};
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template <std::size_t I, typename T, typename ...Ts>
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struct sequence_element<I, type_sequence<T, Ts...>>
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{
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using type = typename sequence_element<I - 1, type_sequence<Ts...>>::type;
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};
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template <typename T, typename ...Ts>
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struct sequence_element<0, type_sequence<T, Ts...>>
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{
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using type = T;
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};
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template <std::size_t I, typename T, T J, T ...Js>
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struct sequence_element<I, std::integer_sequence<T, J, Js...>>
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: std::integral_constant
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<
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T,
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sequence_element<I - 1, std::integer_sequence<T, Js...>>::value
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>
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{};
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template <typename T, T J, T ...Js>
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struct sequence_element<0, std::integer_sequence<T, J, Js...>>
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: std::integral_constant<T, J>
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{};
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template <typename ...Ts>
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struct pack_front
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{
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static_assert(sizeof...(Ts) > 0, "Parameter pack can not be empty.");
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};
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template <typename T, typename ... Ts>
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struct pack_front<T, Ts...>
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{
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typedef T type;
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};
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template <typename Sequence>
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struct sequence_front
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: sequence_element<0, Sequence>
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{
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static_assert(sequence_size<Sequence>::value > 0, "Sequence can not be empty.");
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};
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template <typename Sequence>
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struct sequence_back
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: sequence_element<sequence_size<Sequence>::value - 1, Sequence>
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{
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static_assert(sequence_size<Sequence>::value > 0, "Sequence can not be empty.");
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};
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template <typename Sequence>
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struct sequence_empty
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: std::integral_constant
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<
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bool,
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sequence_size<Sequence>::value == 0
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>
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{};
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// Defines type member for the first type in sequence that satisfies UnaryPred.
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template
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<
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typename Sequence,
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template <typename> class UnaryPred
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>
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struct sequence_find_if {};
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template
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<
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typename T, typename ...Ts,
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template <typename> class UnaryPred
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>
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struct sequence_find_if<type_sequence<T, Ts...>, UnaryPred>
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: std::conditional
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<
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UnaryPred<T>::value,
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T,
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// TODO: prevent instantiation for the rest of the sequence if value is true
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typename sequence_find_if<type_sequence<Ts...>, UnaryPred>::type
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>
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{};
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template <template <typename> class UnaryPred>
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struct sequence_find_if<type_sequence<>, UnaryPred>
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{
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// TODO: This is technically incorrect because void can be stored in a type_sequence
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using type = void;
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};
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// sequence_merge<type_sequence<A, B>, type_sequence<C, D>>::type is
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// type_sequence<A, B, C, D>
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// sequence_merge<integer_sequence<A, B>, integer_sequence<C, D>>::type is
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// integer_sequence<A, B, C, D>
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template <typename ...Sequences>
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struct sequence_merge;
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template <typename S>
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struct sequence_merge<S>
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{
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using type = S;
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};
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template <typename ...T1s, typename ...T2s>
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struct sequence_merge<type_sequence<T1s...>, type_sequence<T2s...>>
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{
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using type = type_sequence<T1s..., T2s...>;
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};
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template <typename T, T ...I1s, T ...I2s>
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struct sequence_merge<std::integer_sequence<T, I1s...>, std::integer_sequence<T, I2s...>>
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{
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using type = std::integer_sequence<T, I1s..., I2s...>;
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};
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template <typename S1, typename S2, typename ...Sequences>
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struct sequence_merge<S1, S2, Sequences...>
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{
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using type = typename sequence_merge
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<
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typename sequence_merge<S1, S2>::type,
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typename sequence_merge<Sequences...>::type
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>::type;
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};
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// sequence_combine<type_sequence<A, B>, type_sequence<C, D>>::type is
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// type_sequence<type_sequence<A, C>, type_sequence<A, D>,
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// type_sequence<B, C>, type_sequence<B, D>>
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template <typename Sequence1, typename Sequence2>
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struct sequence_combine;
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template <typename ...T1s, typename ...T2s>
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struct sequence_combine<type_sequence<T1s...>, type_sequence<T2s...>>
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{
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template <typename T1>
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using type_sequence_t = type_sequence<type_sequence<T1, T2s>...>;
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using type = typename sequence_merge<type_sequence_t<T1s>...>::type;
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};
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// sequence_combine<integer_sequence<T, 1, 2>, integer_sequence<T, 3, 4>>::type is
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// type_sequence<integer_sequence<T, 1, 3>, integer_sequence<T, 1, 4>,
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// integer_sequence<T, 2, 3>, integer_sequence<T, 2, 4>>
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template <typename T, T ...I1s, T ...I2s>
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struct sequence_combine<std::integer_sequence<T, I1s...>, std::integer_sequence<T, I2s...>>
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{
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template <T I1>
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using type_sequence_t = type_sequence<std::integer_sequence<T, I1, I2s>...>;
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using type = typename sequence_merge<type_sequence_t<I1s>...>::type;
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};
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// Selects least element from a parameter pack based on
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// LessPred<T1, T2>::value comparison, similar to std::min_element
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template
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<
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template <typename, typename> class LessPred,
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typename ...Ts
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>
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struct pack_min_element;
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template
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<
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template <typename, typename> class LessPred,
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typename T
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>
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struct pack_min_element<LessPred, T>
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{
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using type = T;
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};
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template
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<
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template <typename, typename> class LessPred,
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typename T1, typename T2
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>
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struct pack_min_element<LessPred, T1, T2>
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{
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using type = std::conditional_t<LessPred<T1, T2>::value, T1, T2>;
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};
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template
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<
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template <typename, typename> class LessPred,
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typename T1, typename T2, typename ...Ts
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>
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struct pack_min_element<LessPred, T1, T2, Ts...>
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{
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using type = typename pack_min_element
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<
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LessPred,
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typename pack_min_element<LessPred, T1, T2>::type,
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typename pack_min_element<LessPred, Ts...>::type
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>::type;
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};
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// Selects least element from a sequence based on
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// LessPred<T1, T2>::value comparison, similar to std::min_element
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template
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<
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typename Sequence,
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template <typename, typename> class LessPred
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>
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struct sequence_min_element;
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template
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<
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typename ...Ts,
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template <typename, typename> class LessPred
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>
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struct sequence_min_element<type_sequence<Ts...>, LessPred>
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{
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using type = typename pack_min_element<LessPred, Ts...>::type;
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};
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// TODO: Since there are two kinds of parameter packs and sequences there probably should be two
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// versions of sequence_find_if as well as parameter_pack_min_element and sequence_min_element.
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// Currently these utilities support only types.
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} // namespace util
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}} // namespace boost::geometry
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#endif // BOOST_GEOMETRY_UTIL_SEQUENCE_HPP
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