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Diffstat (limited to 'src/boost/libs/hana/example/misc/overload_linearly.cpp')
-rw-r--r-- | src/boost/libs/hana/example/misc/overload_linearly.cpp | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/misc/overload_linearly.cpp b/src/boost/libs/hana/example/misc/overload_linearly.cpp new file mode 100644 index 000000000..a41174a27 --- /dev/null +++ b/src/boost/libs/hana/example/misc/overload_linearly.cpp @@ -0,0 +1,42 @@ +// Copyright Louis Dionne 2013-2017 +// Distributed under the Boost Software License, Version 1.0. +// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) + +#include <boost/hana/assert.hpp> +#include <boost/hana/equal.hpp> +#include <boost/hana/find_if.hpp> +#include <boost/hana/optional.hpp> +#include <boost/hana/transform.hpp> +#include <boost/hana/tuple.hpp> +#include <boost/hana/type.hpp> + +#include <string> +namespace hana = boost::hana; + + +// We have an utility in the Functional module that does pretty much the +// same, but is more compile-time efficient. It is still interesting to +// see this implemented with sequences and the SFINAE combinator. + +auto overload_linearly = [](auto ...candidates) { + return [=](auto ...args) { + auto maybe_function = hana::find_if(hana::make_tuple(candidates...), [=](auto f) { + return hana::is_valid(f)(args...); + }); + auto result = hana::transform(maybe_function, [=](auto f) { + return f(args...); + }); + return result; + }; +}; + +int main() { + auto f = ::overload_linearly( + [](std::string s) { return s + "abcd"; }, + [](int i) { return i + 1; }, + [](double f) { return f + 2; } + ); + + BOOST_HANA_RUNTIME_CHECK(f(1) == hana::just(1 + 1)); + BOOST_HANA_RUNTIME_CHECK(f(2.3) == hana::just(static_cast<int>(2.3) + 1)); +} |