find_if.cpp 1.3 KB

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  1. // Copyright Louis Dionne 2013-2017
  2. // Distributed under the Boost Software License, Version 1.0.
  3. // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
  4. #include <boost/hana/assert.hpp>
  5. #include <boost/hana/equal.hpp>
  6. #include <boost/hana/equal.hpp>
  7. #include <boost/hana/ext/std/integral_constant.hpp>
  8. #include <boost/hana/find_if.hpp>
  9. #include <boost/hana/functional/compose.hpp>
  10. #include <boost/hana/optional.hpp>
  11. #include <boost/hana/tuple.hpp>
  12. #include <boost/hana/type.hpp>
  13. #include <type_traits>
  14. namespace hana = boost::hana;
  15. // First get the type of the object, and then call the trait on it.
  16. constexpr auto is_integral = hana::compose(hana::trait<std::is_integral>, hana::typeid_);
  17. constexpr auto is_class = hana::compose(hana::trait<std::is_class>, hana::typeid_);
  18. static_assert(
  19. hana::find_if(hana::make_tuple(1.0, 2, '3'), is_integral) == hana::just(2)
  20. , "");
  21. BOOST_HANA_CONSTANT_CHECK(
  22. hana::find_if(hana::make_tuple(1.0, 2, '3'), is_class) == hana::nothing
  23. );
  24. constexpr auto types = hana::tuple_t<char, int, unsigned, long, unsigned long>;
  25. BOOST_HANA_CONSTANT_CHECK(
  26. hana::find_if(types, hana::equal.to(hana::type_c<unsigned>)) == hana::just(hana::type_c<unsigned>)
  27. );
  28. BOOST_HANA_CONSTANT_CHECK(
  29. hana::find_if(types, hana::equal.to(hana::type_c<void>)) == hana::nothing
  30. );
  31. int main() { }