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Diffstat (limited to 'src/boost/libs/hana/example/tutorial/introspection.sfinae.cpp')
-rw-r--r-- | src/boost/libs/hana/example/tutorial/introspection.sfinae.cpp | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/tutorial/introspection.sfinae.cpp b/src/boost/libs/hana/example/tutorial/introspection.sfinae.cpp new file mode 100644 index 000000000..9b987ff9b --- /dev/null +++ b/src/boost/libs/hana/example/tutorial/introspection.sfinae.cpp @@ -0,0 +1,44 @@ +// 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.hpp> + +#include <string> +#include <vector> +namespace hana = boost::hana; + + +struct yes { std::string toString() const { return "yes"; } }; +struct no { }; + +//! [optionalToString.sfinae] +template <typename T> +std::string optionalToString(T const& obj) { + auto maybe_toString = hana::sfinae([](auto&& x) -> decltype(x.toString()) { + return x.toString(); + }); + + return maybe_toString(obj).value_or("toString not defined"); +} +//! [optionalToString.sfinae] + +int main() { +BOOST_HANA_RUNTIME_CHECK(optionalToString(yes{}) == "yes"); +BOOST_HANA_RUNTIME_CHECK(optionalToString(no{}) == "toString not defined"); + +{ + +//! [maybe_add] +auto maybe_add = hana::sfinae([](auto x, auto y) -> decltype(x + y) { + return x + y; +}); + +maybe_add(1, 2); // hana::just(3) + +std::vector<int> v; +maybe_add(v, "foobar"); // hana::nothing +//! [maybe_add] + +} +} |