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]
+
+}
+}