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example2.cpp
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example2.cpp
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/*
* Tuple Examples
* Copyright (c) 2016 Andreas Herrmann
*
* 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/or sell 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.
*/
#include <cassert>
#include <functional>
#include <tuple>
#include <utility>
using std::get;
using std::index_sequence;
using std::integral_constant;
using std::make_index_sequence;
using std::make_tuple;
using std::plus;
using std::size_t;
using std::tuple_size;
template <class F, size_t... Is>
constexpr auto index_apply_impl(F f,
index_sequence<Is...>) {
return f(integral_constant<size_t, Is> {}...);
}
template <size_t N, class F>
constexpr auto index_apply(F f) {
return index_apply_impl(f, make_index_sequence<N>{});
}
template <size_t N, class Tuple>
constexpr auto take_front(Tuple t) {
return index_apply<N>([&](auto... Is) {
return make_tuple(get<Is>(t)...);
});
}
template <class Tuple, class F>
constexpr auto apply(Tuple t, F f) {
return index_apply<tuple_size<Tuple>{}>(
[&](auto... Is) { return f(get<Is>(t)...); });
}
int main() {
assert(take_front<2>(make_tuple(1, 2, 3, 4)) ==
make_tuple(1, 2));
assert(apply(make_tuple(1, 2), plus<>{}) == 3);
}