type_info_of

Summary: [Folly] `type_info_of`, which returns `typeid` when RTTI is available, otherwise `nullptr`.

Reviewed By: swolchok

Differential Revision: D14159675

fbshipit-source-id: b64ab770f12c7385bb286f658627d085e561def6

folly/detail/StaticSingletonManager.h

@@ -24,6 +24,7 @@
 #include <folly/Likely.h>
 #include <folly/detail/Singleton.h>
 #include <folly/lang/Exception.h>
+#include <folly/lang/TypeInfo.h>
 
 namespace folly {
 namespace detail {
@@ -75,12 +76,12 @@ class StaticSingletonManagerWithRtti {
   }
 
   template <typename T, typename Tag>
-  FOLLY_ALWAYS_INLINE static std::type_info const& key_() {
-#if FOLLY_HAS_RTTI
-    return typeid(TypeTuple<T, Tag>);
-#else
+  FOLLY_ALWAYS_INLINE static Key const& key_() {
+    auto const key = type_info_of<TypeTuple<T, Tag>>();
+    if (!key) {
       throw_exception<std::logic_error>("rtti unavailable");
-#endif
+    }
+    return *key;
   }
 
   FOLLY_NOINLINE static void* create_(Key const& key, Make& make, Cache& cache);

folly/lang/TypeInfo.h

+/*
+ * Copyright 2019-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <typeinfo>
+
+#include <folly/Portability.h>
+
+namespace folly {
+
+//  type_info_of
+//
+//  Returns &typeid(T) if RTTI is available, nullptr otherwise.
+//
+//  This overload works on the static type of the template parameter.
+template <typename T>
+FOLLY_ALWAYS_INLINE static std::type_info const* type_info_of() {
+#if FOLLY_HAS_RTTI
+  return &typeid(T);
+#else
+  return nullptr;
+#endif
+}
+
+//  type_info_of
+//
+//  Returns &typeid(t) if RTTI is available, nullptr otherwise.
+//
+//  This overload works on the dynamic type of the non-template parameter.
+template <typename T>
+FOLLY_ALWAYS_INLINE static std::type_info const* type_info_of(T const& t) {
+#if FOLLY_HAS_RTTI
+  return &typeid(t);
+#else
+  return nullptr;
+#endif
+}
+
+} // namespace folly

folly/lang/test/TypeInfoTest.cpp

+/*
+ * Copyright 2019-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/lang/TypeInfo.h>
+
+#include <folly/portability/GTest.h>
+
+class TypeInfoTest : public testing::Test {};
+
+namespace std {
+static void PrintTo(type_info const& ti, std::ostream* out) {
+  *out << ti.name();
+}
+} // namespace std
+
+namespace {
+struct Foo {};
+struct Bar : Foo {
+  virtual ~Bar() {}
+};
+struct Toc : Bar {};
+} // namespace
+
+TEST_F(TypeInfoTest, exanples) {
+  EXPECT_EQ(typeid(Foo), *folly::type_info_of<Foo>());
+  EXPECT_EQ(typeid(Foo), *folly::type_info_of(Foo()));
+  EXPECT_EQ(typeid(Foo), *folly::type_info_of(static_cast<Foo const&>(Bar())));
+  EXPECT_EQ(typeid(Bar), *folly::type_info_of(static_cast<Bar const&>(Bar())));
+  EXPECT_EQ(typeid(Toc), *folly::type_info_of(static_cast<Bar const&>(Toc())));
+}