Index: webrtc/base/function_view.h |
diff --git a/webrtc/base/function_view.h b/webrtc/base/function_view.h |
new file mode 100644 |
index 0000000000000000000000000000000000000000..6a7c9109ca6d906ff53601799c65b208917200e4 |
--- /dev/null |
+++ b/webrtc/base/function_view.h |
@@ -0,0 +1,70 @@ |
+/* |
+ * Copyright 2016 The WebRTC Project Authors. All rights reserved. |
+ * |
+ * Use of this source code is governed by a BSD-style license |
+ * that can be found in the LICENSE file in the root of the source |
+ * tree. An additional intellectual property rights grant can be found |
+ * in the file PATENTS. All contributing project authors may |
+ * be found in the AUTHORS file in the root of the source tree. |
+ */ |
+ |
+#ifndef WEBRTC_BASE_FUNCTION_VIEW_H_ |
+#define WEBRTC_BASE_FUNCTION_VIEW_H_ |
+ |
+#include <type_traits> |
+#include <utility> |
+ |
+// Just like std::function, FunctionView will wrap any callable and hide its |
+// actual type, exposing only its signature. But unlike std::function, |
+// FunctionView doesn't own its callable---it just points to it. Thus, it's a |
+// good choice mainly as a function argument when the callable argument will |
+// not be called again once the function has returned. |
+// |
+// TODO(kwiberg): FunctionView doesn't work with function pointers, just with |
+// lambdas. It's trivial to work around this by wrapping the function pointer |
+// in a stateless lambda, but it's tedious so it'd be nice to not have to do |
+// it. |
+ |
+namespace rtc { |
+ |
+template <typename T> |
+class FunctionView; // Undefined. |
+ |
+template <typename RetT, typename... ArgT> |
+class FunctionView<RetT(ArgT...)> final { |
+ public: |
+ // This constructor is implicit, so that callers won't have to convert |
+ // lambdas and other callables to FunctionView<Blah(Blah, Blah)> explicitly. |
+ // This is safe because FunctionView is only a reference to the real |
+ // callable. |
+ // |
+ // We jump through some template metaprogramming hoops to ensure that this |
+ // constructor does *not* accept FunctionView arguments. That way, copy |
+ // construction, assignment, swap etc. will all do the obvious thing (because |
+ // they use the implicitly-declared copy constructor and copy assignment), |
+ // and we will never get a FunctionView object that points to another |
+ // FunctionView. |
+ template <typename F, |
+ typename std::enable_if<!std::is_same< |
+ FunctionView, |
+ typename std::remove_cv<typename std::remove_reference< |
+ F>::type>::type>::value>::type* = nullptr> |
+ FunctionView(F&& f) |
+ : f_(&f), call_(Call<typename std::remove_reference<F>::type>) {} |
+ |
+ RetT operator()(ArgT... args) const { |
+ return call_(f_, std::forward<ArgT>(args)...); |
+ } |
+ |
+ private: |
+ template <typename F> |
+ static RetT Call(void* f, ArgT... args) { |
+ return (*static_cast<F*>(f))(std::forward<ArgT>(args)...); |
+ } |
+ void* f_; |
+ RetT (*call_)(void* f, ArgT... args); |
+}; |
+ |
+} // namespace rtc |
+ |
+#endif // WEBRTC_BASE_FUNCTION_VIEW_H_ |