| 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/core/when.hpp> |
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| 6 | namespace hana = boost::hana; |
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| 7 | |
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| 8 | |
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| 9 | template <typename T, typename = hana::when<true>> |
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| 10 | struct base_template; |
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| 11 | |
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| 12 | template <typename T> |
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| 13 | struct base_template<T, hana::when_valid<typename T::first_type>> { }; |
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| 14 | |
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| 15 | template <typename T> |
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| 16 | struct base_template<T, hana::when_valid<typename T::second_type>> { }; |
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| 17 | |
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| 18 | struct First { struct first_type; }; |
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| 19 | struct Second { struct second_type; }; |
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| 20 | |
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| 21 | template struct base_template<First>; |
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| 22 | template struct base_template<Second>; |
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| 23 | |
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| 24 | int main() { } |
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| 25 | |
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