Ah, yeah.  A profobuf "diff" would have to use its own encoding.  You might
define that encoding using protocol buffers, but you really can't use the
original message type's own encoding to represent a diff between two
messages of that type.

On Fri, Nov 13, 2009 at 2:18 PM, Jeremy Leader <jlea...@oversee.net> wrote:

> I think he's saying that he wants support for sparse repeated fields.
> He wants to diff 2 messages (of the same type) producing an output protobuf
> containing only the fields that differ between the 2 inputs.  For a repeated
> field, if the first 100 instances of the field are the same in both input
> messages, and only the 101st instance of the field differs, he wants the
> output message to contain a 101st instance of the repeated field, without
> having to contain the preceding 100 instances.
> I suppose you could define some meta-format that specified that a repeated
> field in the inputs would result in a repeated field in the output
> containing a nested message with an index field and a difference field.
> --
> Jeremy Leader
> jlea...@oversee.net
> Kenton Varda wrote:
>> What do you mean by "represented with their index"?
>> I don't understand the problem.  Why do repeated fields pose a challenge
>> for diffing?
>> On Fri, Nov 13, 2009 at 1:11 AM, Paddy W <patrick.j.wa...@gmail.com<mailto:
>> patrick.j.wa...@gmail.com>> wrote:
>>    I am working on an application that compares two protocol buffers of
>>    the same type for differences and generates a new 'delta' protocol
>>    buffer with only the differences. This works fine for top level fields
>>    but I can not see a way of dealing with repeating fields or nested
>>    messages in a way that avoids including all of the repeating field
>>    entries/nested message fields in the delta. Is it the case that
>>    repeated fields are positional, in that they must all be present, as
>>    opposed to being represented with their index? Is there any way of
>>    approaching this issue or will the idea of 'delta' messages only work
>>    with 'flat' buffer definitions. Any advice would be appreciated.

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