VersionedFile.walk deprecated?

[Aaron Bentley]

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John Yates wrote:
> Nonetheless the reference to exact line
> identity makes me wonder whether the ideas described in this write-up
> -- reconstructed from ancient memories -- of the matching algorithm in
> DSEE and ClearCase have any relevance:

This sounds very similar to the Patience sequence matcher which we will
merge in 0.9.

http://en.wikipedia.org/wiki/Patience_sorting

>   http://www.abridgegame.org/pipermail/darcs-users/2005-April/006561.html
> 
> My sense is that Aaron's concept of line identity is more one of object
> identity.

Right.  When performing a sequence match, I'd prefer to give first
priority to lines that are definitely the same line in both revisions,
second priority to lines that have the same text in both revisions, and
are unique in each, and third priority to non-unique lines.

>  And of course his thread is about merging, not differencing.
> The algorithm I describe is only an elaborate comparison algorithm.  But,
> given an edited file, this algorithm might provide better recovery of line
> identity.

Yes, I think it would behave better than the Python standard sequence
matcher, but not very differently from the Patience one.  Currently,
we've had to disable out-of-order matches, because our merge algorithms
can't cope with moves, but I hope we'll be able to implement a
move-sensitive merge in the future.

Aaron
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