43 lines
1.3 KiB
C++
43 lines
1.3 KiB
C++
// Copyright Louis Dionne 2013-2017
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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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#include <boost/hana/assert.hpp>
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#include <boost/hana/equal.hpp>
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#include <boost/hana/find_if.hpp>
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#include <boost/hana/optional.hpp>
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#include <boost/hana/transform.hpp>
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#include <boost/hana/tuple.hpp>
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#include <boost/hana/type.hpp>
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#include <string>
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namespace hana = boost::hana;
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// We have an utility in the Functional module that does pretty much the
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// same, but is more compile-time efficient. It is still interesting to
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// see this implemented with sequences and the SFINAE combinator.
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auto overload_linearly = [](auto ...candidates) {
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return [=](auto ...args) {
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auto maybe_function = hana::find_if(hana::make_tuple(candidates...), [=](auto f) {
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return hana::is_valid(f)(args...);
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});
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auto result = hana::transform(maybe_function, [=](auto f) {
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return f(args...);
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});
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return result;
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};
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};
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int main() {
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auto f = ::overload_linearly(
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[](std::string s) { return s + "abcd"; },
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[](int i) { return i + 1; },
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[](double f) { return f + 2; }
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);
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BOOST_HANA_RUNTIME_CHECK(f(1) == hana::just(1 + 1));
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BOOST_HANA_RUNTIME_CHECK(f(2.3) == hana::just(static_cast<int>(2.3) + 1));
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}
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