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Postings from July 2009
Citeren Rafael Garcia-Suarez <rgarciasuarez@gmail.com>:
> 2009/7/21 Bram <p5p@perl.wizbit.be>:
>> This seem to happen because given creates a lexical $_. It also happens when
>> for/foreach is used with a lexical $_:
>
> Hmm what ? No, given does not create a lexical $_ :
I didn't look at the code only at the docs and the output :/
from perldoc perlsyn:
'given(EXPR) will assign the value of EXPR to $_ within the lexical
scope of the block, so it's similar to do { my $_ = EXPR; ... }'
the output shows a different reference for $_ in the when block and in
the s1 sub
> from pp_entergiven :
>
> if (PL_op->op_targ == 0) {
> SV ** const defsv_p = &GvSV(PL_defgv);
> *defsv_p = newSVsv(POPs);
> SAVECLEARSV(*defsv_p);
> }
> else
> sv_setsv(PAD_SV(PL_op->op_targ), POPs);
>
> What happens, at first glance, it that List::Util always uses the
> global $_. (an "our $_" in the "first" block should solve the pb).
Then what does in create in pp_entergiven?
Doesn't it modify PL_defgv?
(I have to admit being not familiar enough with the code to really
read/understand it :( )
Adding an our $_ does solve the problem:
With 's1 { our $_; print "\tblock:\t \$_ = " . \$_ . " (value: $_)";
};' the output becomes:
Given/when block:
when-1: $_ = SCALAR(0x942d7f0) (value: 1)
s1: $_ = SCALAR(0x942d500) (value: a)
block: $_ = SCALAR(0x942d500) (value: a)
when-2: $_ = SCALAR(0x942d7f0) (value: 1)
But why is this be nessesary?
If given() does not create a lexical $_ then shouldn't the $_ in the
block be the same as the global $_?
>
> We provide UNDERBAR and dUNDERBAR macros to access the current $_, be
> it lexical or global.
>
> However we don't have (yet) an API to localize the current $_ as
> needed in grep-like functions.
>
> I suppose that code from pp_grepstart could be copied in List::Util to
> solve the bug.
That would only work for the XS version right?
(There is also a Pure Perl version...)
Best regards,
Bram
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