| 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 | |
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| 7 | #include <type_traits> |
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| 8 | namespace hana = boost::hana; |
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| 9 | |
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| 10 | |
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| 11 | template <typename T, typename = hana::when<true>> |
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| 12 | struct base_template; |
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| 13 | |
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| 14 | template <typename T> |
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| 15 | struct base_template<T, hana::when_valid<typename T::value_type>> { |
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| 16 | // something useful... |
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| 17 | }; |
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| 18 | |
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| 19 | int main() { } |
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| 20 | |
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