CxxBackports.hh

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//
// MIT License
// Copyright (c) 2020 Jonathan R. Madsen
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED
// "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
// ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
 
#pragma once
 
#include "PTL/ConsumeParameters.hh"
 
#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
 
/// Backports of C++ language features for use with C++11 compilers
 
namespace PTL
{
// Convenience wrappers
template <typename T>
using decay_t = typename std::decay<T>::type;
 
template <bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;
 
/// Provision of tuple expansion to arguments
namespace impl
{
//--------------------------------------------------------------------------------------//
// Stores a tuple of indices.  Used by tuple and pair, and by bind() to
// extract the elements in a tuple.
template <size_t... Indexes>
struct Index_tuple
{};
 
// Concatenates two Index_tuples.
template <typename Itup1, typename Itup2>
struct Itup_cat;
 
template <size_t... Ind1, size_t... Ind2>
struct Itup_cat<Index_tuple<Ind1...>, Index_tuple<Ind2...>>
{
    using __type = Index_tuple<Ind1..., (Ind2 + sizeof...(Ind1))...>;
};
 
// Builds an Index_tuple<0, 1, 2, ..., NumT-1>.
template <size_t NumT>
struct Build_index_tuple
: Itup_cat<typename Build_index_tuple<NumT / 2>::__type,
           typename Build_index_tuple<NumT - NumT / 2>::__type>
{};
 
template <>
struct Build_index_tuple<1>
{
    using __type = Index_tuple<0>;
};
 
template <>
struct Build_index_tuple<0>
{
    using __type = Index_tuple<>;
};
 
/// Class template integer_sequence
template <typename Tp, Tp... Idx>
struct integer_sequence
{
    using value_type = Tp;
    static constexpr size_t size() noexcept { return sizeof...(Idx); }
};
 
template <typename Tp, Tp NumT, typename ISeq = typename Build_index_tuple<NumT>::__type>
struct Make_integer_sequence;
 
template <typename Tp, Tp NumT, size_t... Idx>
struct Make_integer_sequence<Tp, NumT, Index_tuple<Idx...>>
{
    static_assert(NumT >= 0, "Cannot make integer sequence of negative length");
 
    using __type = integer_sequence<Tp, static_cast<Tp>(Idx)...>;
};
 
/// Alias template make_integer_sequence
template <typename Tp, Tp NumT>
using make_integer_sequence = typename Make_integer_sequence<Tp, NumT>::__type;
 
/// Alias template index_sequence
template <size_t... Idx>
using index_sequence = integer_sequence<size_t, Idx...>;
 
/// Alias template make_index_sequence
template <size_t NumT>
using make_index_sequence = make_integer_sequence<size_t, NumT>;
 
template <typename FnT, typename TupleT, size_t... Idx>
static inline auto
apply(FnT&& _func, TupleT _args, impl::index_sequence<Idx...>)
    -> decltype(std::forward<FnT>(_func)(std::get<Idx>(std::move(_args))...))
{
    // GCC 5.3 warns about unused variable _args when the index sequence is empty
#if defined(__GNUC__) && (__GNUC__ < 6)
    if(sizeof...(Idx) == 0)
    {
        ConsumeParameters(_args);
    }
#endif
    return std::forward<FnT>(_func)(std::get<Idx>(std::move(_args))...);
}
 
//--------------------------------------------------------------------------------------//
 
}  // namespace impl
 
//--------------------------------------------------------------------------------------//
 
template <typename FnT, typename TupleT>
static inline void
apply(FnT&& _func, TupleT&& _args)
{
    using tuple_type = decay_t<TupleT>;
    constexpr auto N = std::tuple_size<tuple_type>::value;
    impl::apply(std::forward<FnT>(_func), std::forward<TupleT>(_args),
                impl::make_index_sequence<N>{});
}
 
}  // namespace PTL