Re: /x treated inconsistently

On 9/23/07, Dave Mitchell <davemiabyn.com> wrote:
> On Sat, Sep 22, 2007 at 08:05:59AM -0700, Chris Dolan
wrote:
> > These should output the same value, but instead
the first one emits
> > "f" and the second one undef.
> >
> >        my $qr = qr/(f)/;
> >        print "#f" =~ m/[#](f)/x;
> >        print "#f" =~ m/[#]$qr/x;
> >
> > This is more revealing:
> >
> >        print qr/[#]$qr/x;
> >
> > yields:
> >
> >        (?x-ism:[#]$qr
> >        )
> >
> > So, it appears that [#] is disabling interpolation
for variables that
> > follow, but then still treating the content as
regexp.  Clearly, it's
> > not *just* treating it as a comment, or the
remaining qr/[/ would be
> > a syntax error.
>
> Hmm, looks like the tokenizer isn't smart enough to
know to ignore #'s
> when within a character class. S_scan_const() needs to
be made even more
> scary than it already is. Probably a post 5.10.0 job.

It is not clear to me that this is a bug actually. The
documentation
states that # must be escaped in an /x pattern afair.

Yves
-- 
perl -Mre=debug -e "/just|another|perl|hacker/"

On Mon, Sep 24, 2007 at 10:05:13AM +0200, demerphq wrote:
> On 9/23/07, Dave Mitchell <davemiabyn.com> wrote:
> > On Sat, Sep 22, 2007 at 08:05:59AM -0700, Chris
Dolan wrote:
> > > These should output the same value, but
instead the first one emits
> > > "f" and the second one undef.
> > >
> > >        my $qr = qr/(f)/;
> > >        print "#f" =~ m/[#](f)/x;
> > >        print "#f" =~ m/[#]$qr/x;
> > >
> > > This is more revealing:
> > >
> > >        print qr/[#]$qr/x;
> > >
> > > yields:
> > >
> > >        (?x-ism:[#]$qr
> > >        )
> > >
> > > So, it appears that [#] is disabling
interpolation for variables that
> > > follow, but then still treating the content
as regexp.  Clearly, it's
> > > not *just* treating it as a comment, or the
remaining qr/[/ would be
> > > a syntax error.
> >
> > Hmm, looks like the tokenizer isn't smart enough
to know to ignore #'s
> > when within a character class. S_scan_const()
needs to be made even more
> > scary than it already is. Probably a post 5.10.0
job.
> 
> It is not clear to me that this is a bug actually. The
documentation
> states that # must be escaped in an /x pattern afair.

But it also says that # isn't special when in a character
class:

    $ ./perl -Dr -e'/[#]a
    b/x'
    Compiling REx "[#]a%nb"
    rarest char # at 0
    Final program:
       1: EXACT <#ab> (5)
       5: END (0)

    $ perl -le'print "ok" if "#" =~
/[#]/x'
    ok
    $



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