SF: Clean up ftl::SmallMap lookup fallbacks
Avoid std::cref to a local variable, which is not intuitive and incurs
construction in the non-fallback case.
Bug: 185536303
Test: ftl_test
Change-Id: I1c5a94bdab105a04f8230fe762bdc433eea5c97a
diff --git a/include/ftl/algorithm.h b/include/ftl/algorithm.h
index c5ff03b..c0f6768 100644
--- a/include/ftl/algorithm.h
+++ b/include/ftl/algorithm.h
@@ -68,4 +68,29 @@
return std::cref(pair.second);
}
+// Combinator for ftl::Optional<T>::or_else when T is std::reference_wrapper<const V>. Given a
+// lambda argument that returns a `constexpr` value, ftl::static_ref<T> binds a reference to a
+// static T initialized to that constant.
+//
+// const ftl::SmallMap map = ftl::init::map(13, "tiramisu"sv)(14, "upside-down cake"sv);
+// assert("???"sv ==
+// map.get(20).or_else(ftl::static_ref<std::string_view>([] { return "???"sv; }))->get());
+//
+// using Map = decltype(map);
+//
+// assert("snow cone"sv ==
+// ftl::find_if(map, [](const auto& pair) { return pair.second.front() == 's'; })
+// .transform(ftl::to_mapped_ref<Map>)
+// .or_else(ftl::static_ref<std::string_view>([] { return "snow cone"sv; }))
+// ->get());
+//
+template <typename T, typename F>
+constexpr auto static_ref(F&& f) {
+ return [f = std::forward<F>(f)] {
+ constexpr auto kInitializer = f();
+ static const T kValue = kInitializer;
+ return Optional(std::cref(kValue));
+ };
+}
+
} // namespace android::ftl