Re: my git problem

From: J. Bruce Fields <bfields@fieldses.org>
Date: Apr 29, 2008, 17:15 UTC
Message-ID: <20080429171519.GA21310@fieldses.org>
In-Reply-To: <alpine.LFD.1.10.0804281222190.3119@woody.linux-foundation.org>

On Mon, Apr 28, 2008 at 12:28:38PM -0700, Linus Torvalds wrote:

Show 15 quoted lines

> 
> 
> On Mon, 28 Apr 2008, Johannes Schindelin wrote:
> > 
> > On Mon, 28 Apr 2008, Andrew Morton wrote:
> > > 
> > > That's missing the "logical" bit :)
> > 
> > Heh, you're right.  I am too used to Git to think how other people would 
> > feel about these things... :-)
> 
> No, you are both wrong.
> 
> You're wrong because apparently you never did abstract algebra and set 
> theory in school.

Hmph. I've got a PhD in algebra and still find that choice of operators confusing.

(Which may just be further evidence that one can take a lot of classes and still be an idiot.)

Show 10 quoted lines

> If you know math, git actually does the rigth and very much the *logical* 
> thing.
> 
> So ".." is a simple difference, while "..." is a more complex difference. 
> 
> They mean different things for different operation types, but that is 
> again something a math person takes for granted (ie in algebra, a "+" or 
> "-" is just a random operation that follows certain rules: "a-b" means one 
> thing for the set of real numbers, and something *totally* different if 
> you are talking about set algebra).

I suspect one reason the set-difference operator is more commonly written with a backslash than a minus sign is that set difference is different enough from anything else usually called subtraction that most people find it confusing to use the same notation.

I can sorta buy the argument that "A...B" means most generally "some kind of difference between the three sets A, A^B, and B", and that in the context of "git diff" it's most sensible to take ordering into account and produce some approximation of a diff between A^B and B. I'd personally have found an entirely separate operator simpler to understand. But perhaps there's only so many keys on the keyboard.

--b.