| 1 | // Copyright Louis Dionne 2013-2022 |
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| 2 | // Distributed under the Boost Software License, Version 1.0. |
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| 3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 4 | |
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| 5 | #include <boost/hana/functional/arg.hpp> |
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| 6 | |
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| 7 | #include <cstddef> |
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| 8 | #include <utility> |
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| 9 | namespace hana = boost::hana; |
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| 10 | |
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| 11 | |
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| 12 | constexpr int to_int(char c) |
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| 13 | { return static_cast<int>(c) - 48; } |
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| 14 | |
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| 15 | template <std::size_t N> |
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| 16 | constexpr long long parse(const char (&arr)[N]) { |
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| 17 | long long number = 0, base = 1; |
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| 18 | for (std::size_t i = 0; i < N; ++i) { |
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| 19 | number += to_int(arr[N - 1 - i]) * base; |
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| 20 | base *= 10; |
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| 21 | } |
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| 22 | return number; |
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| 23 | } |
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| 24 | |
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| 25 | template <char ...c> |
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| 26 | struct pick { |
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| 27 | static constexpr unsigned long n = parse<sizeof...(c)>({c...}); |
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| 28 | |
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| 29 | template <typename ...T> |
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| 30 | constexpr auto operator()(T&& ...args) const |
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| 31 | { return hana::arg<n>(std::forward<T>(args)...); } |
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| 32 | }; |
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| 33 | |
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| 34 | template <char ...c> constexpr pick<c...> operator"" _st() { return {}; } |
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| 35 | template <char ...c> constexpr pick<c...> operator"" _nd() { return {}; } |
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| 36 | template <char ...c> constexpr pick<c...> operator"" _rd() { return {}; } |
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| 37 | template <char ...c> constexpr pick<c...> operator"" _th() { return {}; } |
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| 38 | |
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| 39 | |
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| 40 | static_assert(1_st(1, '2', 3.3, 444) == 1, "" ); |
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| 41 | static_assert(2_nd(1, '2', 3.3, 444) == '2', "" ); |
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| 42 | static_assert(3_rd(1, '2', 3.3, 444) == 3.3, "" ); |
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| 43 | static_assert(4_th(1, '2', 3.3, 444) == 444, "" ); |
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| 44 | |
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| 45 | int main() { } |
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| 46 | |
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