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48 lines
1.1 KiB
C++
48 lines
1.1 KiB
C++
/*
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@copyright Louis Dionne 2014
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#include <boost/hana/detail/constexpr.hpp>
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#include <boost/hana/detail/static_assert.hpp>
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#include <boost/hana/maybe.hpp>
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#include <string>
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#include <type_traits>
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using namespace boost::hana;
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template <typename F>
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struct _sfinae {
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F f;
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template <typename ...X>
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constexpr auto call(int, X ...x) const -> decltype(just(f(x...)))
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{ return just(f(x...)); }
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template <typename ...X>
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constexpr auto call(long, X...) const
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{ return nothing; }
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template <typename ...X>
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constexpr auto operator()(X ...x) const
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{ return call(int{0}, x...); }
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};
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BOOST_HANA_CONSTEXPR_LAMBDA auto sfinae = [](auto f) {
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return _sfinae<decltype(f)>{f};
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};
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int main() {
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auto f = sfinae([](auto x) -> decltype(x + 1) {
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return x + 1;
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});
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BOOST_HANA_STATIC_ASSERT(f(1) == just(2));
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BOOST_HANA_STATIC_ASSERT(f(std::string{"abc"}) == nothing);
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BOOST_HANA_STATIC_ASSERT(bind(just(1), f) == just(2));
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}
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