Mojo C++ bindings: Generate InterfaceHandle<> instead of InterfacePtr<>.

mojo/public/cpp/bindings/interface_handle.h

 // Copyright 2015 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_INTERFACE_PTR_INFO_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_PTR_INFO_H_
 
+#include <cstddef>
+
 #include "mojo/public/cpp/system/macros.h"
 #include "mojo/public/cpp/system/message_pipe.h"
 
 namespace mojo {
 
+template <typename Interface>
+class InterfacePtr;
+
 // InterfaceHandle stores necessary information to communicate with a remote
 // interface implementation, which could be used to construct an InterfacePtr.
 template <typename Interface>
 class InterfaceHandle {
  public:
   InterfaceHandle() : version_(0u) {}
+  InterfaceHandle(std::nullptr_t) : version_(0u) {}
 
   InterfaceHandle(ScopedMessagePipeHandle handle, uint32_t version)
       : handle_(handle.Pass()), version_(version) {}
 
   InterfaceHandle(InterfaceHandle&& other)
       : handle_(other.handle_.Pass()), version_(other.version_) {
     other.version_ = 0u;
   }
 
+  // Making this constructor templated ensures that it is not type-instantiated
+  // unless it is used, making the InterfacePtr<->InterfaceHandle codependency
+  // less fragile.
+  template <typename SameInterfaceAsAbove>

[viettrungluu, 2016/02/11 18:26:29]

If you want to make it clearer that users probably shouldn't given a type
parameter, I'd give SameInterfaceAsAbove a default value (namely, |Interface|).

[vardhan, 2016/02/11 22:47:53]

Done.

+  InterfaceHandle(InterfacePtr<SameInterfaceAsAbove>&& ptr) {
+    *this = ptr.PassInterfaceHandle();
+  }
+
   ~InterfaceHandle() {}
 
   InterfaceHandle& operator=(InterfaceHandle&& other) {
     if (this != &other) {
       handle_ = other.handle_.Pass();
       version_ = other.version_;
       other.version_ = 0u;
     }
 
     return *this;
   }
 
+  // Tests as true if we have a valid handle.
+  explicit operator bool() const { return is_valid(); }
   bool is_valid() const { return handle_.is_valid(); }
 
   ScopedMessagePipeHandle PassHandle() { return handle_.Pass(); }
   const ScopedMessagePipeHandle& handle() const { return handle_; }
   void set_handle(ScopedMessagePipeHandle handle) { handle_ = handle.Pass(); }
 
   uint32_t version() const { return version_; }
   void set_version(uint32_t version) { version_ = version; }
 
  private:
   ScopedMessagePipeHandle handle_;
   uint32_t version_;
 
   MOJO_MOVE_ONLY_TYPE(InterfaceHandle);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_PTR_INFO_H_