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
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+++ b/src/boost/libs/hana/example/misc/overload_linearly.cpp
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+// 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));
+}