Re: Localization method of $1

[Peter Scott <Peter@PSDT.com>]

At 01:02 PM 1/15/00 -0500, Jeff Pinyan wrote:
>On Jan 15, Peter Scott said:
> > $_ = "abc";
> > print   "Before setting:  ", pref $1;
> > s/(ab)/bar($1)/e;
> > print   "After s///:      ", pref $1;
> >
> > sub bar {
> >    $_[0] =~ /(b)/;
> >    print "Inside /e sub:   ", pref $1;
> >    print "Original \$1 now: ", pref $_[0];
> > # Note: attempt to assign to $_[0] here generates
> > # "Modification of a read-only value"
> > }
>
>That's because $_[0] is /really, truly/ $1.
>
>   @_ = ("new thing") ;
>
>Will not affect $1.  Assigning to a specific index of @_ will modify the
>variable that was passed to the function in that position (see the code
>below).  [code showing that @_ is aliased to the inputs snipped]

I'm aware of this.  I noted that attempts to assign anything to $_[0] fail 
with a read-only variable error.

I'm not assigning anything to $_[0] - I'm just binding it to a regex.  The 
results I posted show that the effect of this is to overwrite the original 
$1 that was passed in, even though some kind of localization happened which 
caused its value to be restored after the subroutine returned.

'Localization' to me means, "created a new version of this variable at a 
new location, leaving the old one alone until we exit the current scope," 
and that's what happened with the example I posted using 'local'.  But the 
way perl localized $1 appears to be different.

--
Peter Scott
Pacific Systems Design Technologies

---

Follow-Ups from:

Ilya Zakharevich <ilya@math.ohio-state.edu>

References to:

Peter Scott <Peter@PSDT.com>
Jeff Pinyan <jeffp@crusoe.net>

---

[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index][Thread Index][Top&Search][Original]

---