Adds base::WrapFunction to wrap lambdas as base::Callbacks

base/function_util.h

Index: base/function_util.h
diff --git a/base/function_util.h b/base/function_util.h
new file mode 100644
index 0000000000000000000000000000000000000000..1598804aa73e760407413fdef27e505f402becb4
--- /dev/null
+++ b/base/function_util.h
@@ -0,0 +1,67 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_FUNCTION_UTIL_H_
+#define BASE_FUNCTION_UTIL_H_
+
+#include <utility>
+
+#include "base/bind.h"
+#include "base/callback.h"
+
+namespace base {
+
+namespace internal {
+
+template <typename FuncType, typename Result, typename... Args>
+struct FunctionBinderHelper {
+  static Result Run(FuncType func, Args... args) {

[yzshen1, 2016/06/22 23:05:54]

Do we need Args&&... (here and below)?

[Ken Rockot(use gerrit already), 2016/06/22 23:14:43]

This wouldn't work - we can't for example base::Bind a function with a signature
void(Foo&&) and get a base::Callback<void(Foo)>.

+    return func(std::forward<Args>(args)...);
+  }
+};
+
+template <typename FuncType, typename... Args>
+struct FunctionBinderHelper<FuncType, void, Args...> {
+  static void Run(FuncType func, Args... args) {
+    func(std::forward<Args>(args)...);
+  }
+};
+
+template <typename CallbackType>
+struct FunctionBinder {};
+
+template <typename ResultType, typename... Args>
+struct FunctionBinder<Callback<ResultType(Args...)>> {
+  template <typename FuncType>
+  static Callback<ResultType(Args...)> BindFunction(FuncType func) {
+    return Bind(
+        &FunctionBinderHelper<FuncType, ResultType, Args...>::Run, func);
+  }
+};
+
+}  // namespace internal
+
+// Wraps an arbitrary function as a base::Callback. Note that this requires an
+// explicit specification of the target base::Callback type, but the wrapped
+// function type can be inferred and thus supports wrapping C++11 lambdas.
+//
+// For example:
+//
+//   using AddCallback = base::Callback<int(int x, int y)>;
+//   AddCallback cb = base::WrapLambda<AddCallback>([](int x, int y) {
+//     return x + y;
+//   });
+//   int z = cb.Run(x, y);
+//
+// NOTE: Do NOT wrap lambdas which capture references of any kind unless it is
+// abundantly clear that this will not lead to subtle bugs, e.g., the wrapped
+// callback cannot possibly outlive the captured references.
+template <typename CallbackType, typename FuncType>
+CallbackType WrapFunction(FuncType func) {
+  return internal::FunctionBinder<CallbackType>::BindFunction(func);
+}
+
+}  // namespace base
+
+#endif  // BASE_FUNCTION_UTIL_H_