Re: [PATCH 2/3] merge-recursive: make empty tree a known object

[Linus Torvalds <torvalds@osdl.org>]

On Sun, 10 Dec 2006, Junio C Hamano wrote:
> 
> That is fine by me.  We would benefit from an empty blob and an
> empty tree.

I was wondering if we ever had any special case where we wanted the empty 
blob, and couldn't come up with any. Unlike the "tree diff" case, a "blob 
diff" will not actually do a "real diff" with a non-existing object, it 
special-cases it (and, for performance reasons, I think it really should). 

And all the blob-diff routines generally want to be able to take explicit 
data anyway, not just diffing two SHA1's (since we often don't have a SHA1 
anyway - the working tree case).

So while I think it would make sense to have both the "empty tree" and the 
"empty blob" as special cases, off-hand I can't actually see where we'd 
ever use the empty blob SHA1.

In contrast, the empty tree clearly ends up being an interesting special 
case that actually gets used occasionally, ie here we had two independent 
uses for the same thing..

But maybe somebody can point to a case where we actually would want to 
internally have an easy representation of "empty blob".