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List:       subversion-dev
Subject:    Re: svn commit: r21682 - in trunk: subversion/libsvn_ra_svn www
From:       Karl Fogel <kfogel () google ! com>
Date:       2006-09-29 21:08:01
Message-ID: janven6pej2.fsf () morbius ! corp ! google ! com
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Daniel Rall <dlr@collab.net> writes:
> On Wed, 27 Sep 2006, kfogel@tigris.org wrote:
> ....
>> --- trunk/subversion/libsvn_ra_svn/protocol	(original)
>> +++ trunk/subversion/libsvn_ra_svn/protocol	Wed Sep 27 12:04:02 2006
> ...
>> +4.1. Extending existing commands
>> +
>> +Extending an existing command is normally done by indicating that its
>> +tuple is allowed to end where it currently ends, for backwards
>> +compatibility, and then tacking on a new, possibly optional, tuple.
>> +For example, set-path was extended to include lock-tokens like this:
>> +
>> +  /* OLD */ set-path:
>> +    params: ( path:string rev:number start-empty:bool )
>> +
>> +  /* NEW */ set-path:
>> +    params: ( path:string rev:number start-empty:bool ? [ lock-token:string ] )
>> +
>> +The "?" says that the outer tuple is allowed to end here, because an
>> +old client or server wouldn't know to send the new subtuple.  The new
>> +subtuple appears in square braces because, even in the new protocol,
>> +the lock-token is still optional (but if there's no lock-token to
>> +send, then an empty tuple must still be transmitted, so that future
>> +extensions to this command remain possible).  And if lock-token were
>> +mandatory in the new protocol, then the braces would be parentheses
>> +instead.
>
> We probably want to indicate that optional arguments (as tuple
> contents) for *new* commands need not use the "?" character before the
> "(?x)" sequence, but should use that latter sequence to allow more
> parameters to easily be added at the end of the command.

Can you say that in more words?  I'm not quite catching it...

-Karl


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