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// Boost.Geometry
// Copyright (c) 2020, Oracle and/or its affiliates.
// Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
// Licensed under the Boost Software License version 1.0.
// http://www.boost.org/users/license.html
#ifndef BOOST_GEOMETRY_UTIL_SEQUENCE_HPP
#define BOOST_GEOMETRY_UTIL_SEQUENCE_HPP
#include <type_traits>
namespace boost { namespace geometry
{
namespace util
{
// An alternative would be to use std:tuple and std::pair
// but it would add dependency.
template <typename ...Ts>
struct type_sequence {};
// true if T is a sequence
template <typename T>
struct is_sequence : std::false_type {};
template <typename ...Ts>
struct is_sequence<type_sequence<Ts...>> : std::true_type {};
template <typename T, T ...Is>
struct is_sequence<std::integer_sequence<T, Is...>> : std::true_type {};
// number of elements in a sequence
template <typename Sequence>
struct sequence_size {};
template <typename ...Ts>
struct sequence_size<type_sequence<Ts...>>
: std::integral_constant<std::size_t, sizeof...(Ts)>
{};
template <typename T, T ...Is>
struct sequence_size<std::integer_sequence<T, Is...>>
: std::integral_constant<std::size_t, sizeof...(Is)>
{};
// element of a sequence
template <std::size_t I, typename Sequence>
struct sequence_element {};
template <std::size_t I, typename T, typename ...Ts>
struct sequence_element<I, type_sequence<T, Ts...>>
{
typedef typename sequence_element<I - 1, type_sequence<Ts...>>::type type;
};
template <typename T, typename ...Ts>
struct sequence_element<0, type_sequence<T, Ts...>>
{
typedef T type;
};
template <std::size_t I, typename T, T J, T ...Js>
struct sequence_element<I, std::integer_sequence<T, J, Js...>>
: std::integral_constant
<
T,
sequence_element<I - 1, std::integer_sequence<T, Js...>>::value
>
{};
template <typename T, T J, T ...Js>
struct sequence_element<0, std::integer_sequence<T, J, Js...>>
: std::integral_constant<T, J>
{};
template <typename Sequence>
struct sequence_front
: sequence_element<0, Sequence>
{
static_assert(sequence_size<Sequence>::value > 0, "Sequence can not be empty.");
};
template <typename Sequence>
struct sequence_back
: sequence_element<sequence_size<Sequence>::value - 1, Sequence>
{
static_assert(sequence_size<Sequence>::value > 0, "Sequence can not be empty.");
};
template <typename Sequence>
struct sequence_empty
: std::integral_constant
<
bool,
sequence_size<Sequence>::value == 0
>
{};
template
<
typename Sequence,
template <typename> class UnaryPred
>
struct sequence_find_if {};
template
<
typename T, typename ...Ts,
template <typename> class UnaryPred
>
struct sequence_find_if<type_sequence<T, Ts...>, UnaryPred>
: std::conditional
<
UnaryPred<T>::value,
T,
// TODO: prevent instantiation for the rest of the sequence if value is true
typename sequence_find_if<type_sequence<Ts...>, UnaryPred>::type
>
{};
template <template <typename> class UnaryPred>
struct sequence_find_if<type_sequence<>, UnaryPred>
{
// TODO: This is technically incorrect because void can be stored in a type_sequence
typedef void type;
};
// merge<type_sequence<A, B>, type_sequence<C, D>>::type is
// type_sequence<A, B, C, D>
// merge<integer_sequence<A, B>, integer_sequence<C, D>>::type is
// integer_sequence<A, B, C, D>
template <typename ...Sequences>
struct merge;
template <typename S>
struct merge<S>
{
typedef S type;
};
template <typename ...T1s, typename ...T2s>
struct merge<type_sequence<T1s...>, type_sequence<T2s...>>
{
typedef type_sequence<T1s..., T2s...> type;
};
template <typename T, T ...I1s, T ...I2s>
struct merge<std::integer_sequence<T, I1s...>, std::integer_sequence<T, I2s...>>
{
typedef std::integer_sequence<T, I1s..., I2s...> type;
};
template <typename S1, typename S2, typename ...Sequences>
struct merge<S1, S2, Sequences...>
{
typedef typename merge
<
typename merge<S1, S2>::type,
typename merge<Sequences...>::type
>::type type;
};
// combine<type_sequence<A, B>, type_sequence<C, D>>::type is
// type_sequence<type_sequence<A, C>, type_sequence<A, D>,
// type_sequence<B, C>, type_sequence<B, D>>
template <typename Sequence1, typename Sequence2>
struct combine;
template <typename ...T1s, typename ...T2s>
struct combine<type_sequence<T1s...>, type_sequence<T2s...>>
{
template <typename U1, typename ...U2s>
using type_sequence_t = type_sequence<type_sequence<U1, U2s>...>;
typedef typename merge
<
type_sequence_t<T1s, T2s...>...
>::type type;
};
// combine<integer_sequence<T, 1, 2>, integer_sequence<T, 3, 4>>::type is
// type_sequence<integer_sequence<T, 1, 3>, integer_sequence<T, 1, 4>,
// integer_sequence<T, 2, 3>, integer_sequence<T, 2, 4>>
template <typename T, T ...I1s, T ...I2s>
struct combine<std::integer_sequence<T, I1s...>, std::integer_sequence<T, I2s...>>
{
template <T J1, T ...J2s>
using type_sequence_t = type_sequence<std::integer_sequence<T, J1, J2s>...>;
typedef typename merge
<
type_sequence_t<I1s, I2s...>...
>::type type;
};
// Selects least element from a parameter pack based on
// LessPred<T1, T2>::value comparison, similar to std::min_element
template
<
template <typename, typename> class LessPred,
typename ...Ts
>
struct select_pack_element;
template
<
template <typename, typename> class LessPred,
typename T
>
struct select_pack_element<LessPred, T>
{
typedef T type;
};
template
<
template <typename, typename> class LessPred,
typename T1, typename T2
>
struct select_pack_element<LessPred, T1, T2>
{
typedef std::conditional_t<LessPred<T1, T2>::value, T1, T2> type;
};
template
<
template <typename, typename> class LessPred,
typename T1, typename T2, typename ...Ts
>
struct select_pack_element<LessPred, T1, T2, Ts...>
{
typedef typename select_pack_element
<
LessPred,
typename select_pack_element<LessPred, T1, T2>::type,
typename select_pack_element<LessPred, Ts...>::type
>::type type;
};
// Selects least element from a sequence based on
// LessPred<T1, T2>::value comparison, similar to std::min_element
template
<
typename Sequence,
template <typename, typename> class LessPred
>
struct select_element;
template
<
typename ...Ts,
template <typename, typename> class LessPred
>
struct select_element<type_sequence<Ts...>, LessPred>
{
typedef typename select_pack_element<LessPred, Ts...>::type type;
};
// Selects least pair sequence of elements from a parameter pack based on
// LessPred<xxx_sequence<T11, T12>, xxx_sequence<T21, T22>>::value comparison
template
<
typename Sequence1,
typename Sequence2,
template <typename, typename> class LessPred
>
struct select_combination_element
{
typedef typename select_element
<
typename combine<Sequence1, Sequence2>::type,
LessPred
>::type type;
};
} // namespace util
}} // namespace boost::geometry
#endif // BOOST_GEOMETRY_UTIL_SEQUENCE_HPP
|
