Re: [PATCH] [Outreachy] git/userdiff.c fix regex pattern error

[Junio C Hamano <gitster@pobox.com>]

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> On Sun, 7 Oct 2018, Junio C Hamano wrote:
>
>> And then there is an unnamed misdesigned language that has a
>> regmatch() function, which takes a string that contains a regular
>> expression, but somehow requires that string to begin and end with a
>> slash for no justifiable reason ;-).
>
> It makes more sense once you realize that /<regexp>/ is a very nice
> syntactic construct to obtain an instance of a regular expression object,
> rather than a string describing one.

In Perl, qr/<regexp>/ is often how you use that syntactic construct.

The unnamed misdesigned language literally uses a string whose
content is /<regexp>/; iow, 

	preg_match('/a.*b/', ...)

is what you see, and there is no "regex object involved.  As far as
the function is concerned, it is receiving a string, that represents
a regexp.  There is no reason to require the pattern _string_ to
begin and end with slash, but somehow they do.

> But in C, we do not have objects, so the way to describe a regular
> expression is a string (which you have to compile into an opaque data
> structure before applying it).

Absolutely.  C does not have regexp object literal and the literal
you write to represent a regexp is just a string that you would pass
to functions like regcomp().  But at least C is not so brain-dead to
require slashes on either end of that string ;-)