From: Tay Ray Chuan <rctay89@gmail.com>
Date: Thu, 12 Jan 2012 00:52:49 GMT
Subject: Re: [PATCH 2/2] diff --word-diff: use non-whitespace regex by default
Message-ID: <CALUzUxo3DcKqC6sQFQ1Oi0vgASFSHCcmOgHAj2_4c3vEjy663w@mail.gmail.com>
In-Reply-To: <87lipexawp.fsf@thomas.inf.ethz.ch>

Hi,

Thomas, first off, thanks for looking through this.

On Thu, Jan 12, 2012 at 4:05 AM, Thomas Rast <trast@student.ethz.ch> wrote:
> Tay Ray Chuan <rctay89@gmail.com> writes:
>
>> Factor out the comprehensive non-whitespace regex in use by PATTERNS and
>> IPATTERN and use it as the word-diff regex for the default diff driver.
>
> Why?
>
> I seem to recall that the motivation for keeping the original code as-is
> instead of just emulating its behavior with a default regex was that it
> is faster.  So disabling the default mode should at least have an
> advantage?
>
> </devils-advocate>

If you're talking about speed, yeah, that's probably true.

But I think it's worthwhile to trade-off performance for a sensible
default. Something like

  matrix[a,b,c]
  matrix[d,b,c]

gives

  matrix[[-a-]{+d+},b,c]

and when we have

  ImagineALanguageLikeFoo
  ImagineALanguageLikeBar

we get

  ImagineALanguageLike[-Foo-]{+Bar+}

(But I cheated. Foo and Bar have no common characters in common; if
they did, the word diff would be messy.)

Both of which seem sensible. From a usability/effectiveness
standpoint, I think it's more useful than what the current word-diff
defaults to - the whole line is taken as a "word", with the pre-image
shown as deleted and the post-image as added; we don't even try to run
LCS on it.

Examples are lifted from:
[1] http://article.gmane.org/gmane.comp.version-control.git/105896
[2] http://article.gmane.org/gmane.comp.version-control.git/105237

-- 
Cheers,
Ray Chuan