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- // Copyright Louis Dionne 2013-2017
- // Distributed under the Boost Software License, Version 1.0.
- // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
- #include <boost/hana/functional/arg.hpp>
- #include <cstddef>
- #include <utility>
- namespace hana = boost::hana;
- constexpr int to_int(char c)
- { return static_cast<int>(c) - 48; }
- template <std::size_t N>
- constexpr long long parse(const char (&arr)[N]) {
- long long number = 0, base = 1;
- for (std::size_t i = 0; i < N; ++i) {
- number += to_int(arr[N - 1 - i]) * base;
- base *= 10;
- }
- return number;
- }
- template <char ...c>
- struct pick {
- static constexpr unsigned long n = parse<sizeof...(c)>({c...});
- template <typename ...T>
- constexpr auto operator()(T&& ...args) const
- { return hana::arg<n>(std::forward<T>(args)...); }
- };
- template <char ...c> constexpr pick<c...> operator"" _st() { return {}; }
- template <char ...c> constexpr pick<c...> operator"" _nd() { return {}; }
- template <char ...c> constexpr pick<c...> operator"" _rd() { return {}; }
- template <char ...c> constexpr pick<c...> operator"" _th() { return {}; }
- static_assert(1_st(1, '2', 3.3, 444) == 1, "");
- static_assert(2_nd(1, '2', 3.3, 444) == '2', "");
- static_assert(3_rd(1, '2', 3.3, 444) == 3.3, "");
- static_assert(4_th(1, '2', 3.3, 444) == 444, "");
- int main() { }
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