c++ extension question

[Wade Berrier]

Hi,

Given the following:

----------------------
message MessageContainer {
optional string common_header_info = 1 [default = ""];
extensions 1000 to max;
}

message SubMessage
{
optional string mySubString = 1;
}

extend MessageContainer
{
optional SubMessage subMessage = 1001;
}

----------------------

If I have a Message* (which is actually a SubMessage), how to I set or
copy that extension into MessageContainer, without knowing that the
Message* is a SubMessage?

It looks like all extensions accessors need to use
ExtensionIdentifiers. Is the above possible?

The idea is that I'll use MessageContainer to contain one of several
messages that extend MessageContainer, but I want to have generic code
that doesn't have to know what type of Message is being dealt with.
And I want the code that deals with Messages not to have to worry
about the MessageContainer message.

Another question: is it possible to set an extension message without
making a copy of the message? I read a post about MutableExtension
being designed the way it was because object ownership is clear. But,
I'd hate to have to make a copy if it's not necessary.

Any help/feedback would be greatly appreciated.

Wade

[Kenton Varda]

If you have the FieldDescriptor representing the extension, you can use the container's Reflection interface to do it:

  container.GetReflection()->MutableMessage(&container, descriptor)->CopyFrom(*message);

Nope, you have to copy.  The way to avoid copies is to construct the message in-place in the first place.

 

Any help/feedback would be greatly appreciated.

Wade

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