1 files changed, 53 insertions, 0 deletions
diff --git a/mojo/public/cpp/bindings/lib/callback_internal.h b/mojo/public/cpp/bindings/lib/callback_internal.h
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+++ b/mojo/public/cpp/bindings/lib/callback_internal.h
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+// Copyright 2014 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 MOJO_PUBLIC_CPP_BINDINGS_LIB_CALLBACK_INTERNAL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_CALLBACK_INTERNAL_H_
+
+#include "mojo/public/cpp/bindings/lib/template_util.h"
+
+namespace mojo {
+class String;
+
+namespace internal {
+
+template <typename T>
+struct Callback_ParamTraits {
+  typedef T ForwardType;
+};
+
+template <>
+struct Callback_ParamTraits<String> {
+  typedef const String& ForwardType;
+};
+
+template <typename T, typename... Args>
+struct HasCompatibleCallOperator {
+  // This template's second parameter is the signature of the operator()
+  // overload we want to try to detect:
+  //   void operator()(Args...) const;
+  template <typename U,
+            void (U::*)(
+                typename internal::Callback_ParamTraits<Args>::ForwardType...)
+                const>
+  struct TestType {};
+
+  // This matches type U if it has a call operator with the
+  // expected signature.
+  template <typename U>
+  static YesType Test(TestType<U, &U::operator()>*);
+
+  // This matches anything else.
+  template <typename U>
+  static NoType Test(...);
+
+  // HasCompatibleCallOperator<T, Args...>::value will be true if T has a
+  // compatible call operator.
+  enum { value = (sizeof(Test<T>(nullptr)) == sizeof(YesType)) };
+};
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_CALLBACK_INTERNAL_H_