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Re: Proposal: include var name in 'use of undefined value' warning

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Dave Mitchell
May 11, 2003 04:17
Re: Proposal: include var name in 'use of undefined value' warning
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On Sun, May 11, 2003 at 11:16:35AM +0100, Nick Ing-Simmons wrote:
> Dave Mitchell <> writes:
> >> >Any gotchas?
> >> A. How deep do you search?  - if expression is deep and involves lots
> >>    of closures or whatever this could take a while if 1st 100,000 
> >>    variables are all defined.
> >
> >The search is a shallowish search of the kids of the offending op.
> >Closures etc shouldn't make a difference, as its not searching pads, its
> >searching ops. It should only check a couple of vars for a binary op.
> So when doing this:
>     my $j = 10;
>     $foo = sub { shift(@_) + $j };
>     $result = (($a+$b)*($c+$d))+(($g+$h)* &$foo($i));
> and $i is undef - you find undef scanning the '+' op in the closure 
> but don't know it is $i?

Yeah, in that particular case, the op raising the warning is the '+' in
the sub, so it will see an OP_ SHIFT and give up on that branch,  then
it'll see an OP_PADSV for $j with a valid value, and give up altogether.
It's possible it might handle an OP_AELEMFAST, so { $_[0] + $j } might be
able to say 'uninitialized value $_[0]'.

But in general the rule is: if the var is close at hand and can be
identified, report it; otherwise revert to the old behaviour.

Any [programming] language that doesn't occasionally surprise the
novice will pay for it by continually surprising the expert.
 - Larry Wall

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