Re^2: Perl leve control of hash iterators


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Re^2: Perl leve control of hash iterators

by bsb (Priest)

on Feb 28, 2007 at 04:05 UTC ( [id://602448]=note: print w/replies, xml )

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in reply to Re: Perl leve control of hash iterators
in thread Perl level control of hash iterators

Just to clarify (for all respondants) I'm investigating a bug in Data::Rmap where the following loops off forever:

perl -MData::Rmap=rmap_hash -le 'rmap_hash {print keys %{$_->{a}} } ({
+a=>{1,2}})'
[download]

I'm not certain, but I suspect that the keys call interacts with this line, from Data::Rmap:

push @return, $self->_rmap($_) for values %$_;
[download]

Since the module is for general use, XS or tie-ing aren't really options. Also, $_ is aliased during the callback so that things, including hashes can be changed (sometimes leading to different disasters). This further constrains the solution space.

Thanks for your tips,

Brad

Update: I think autovivification is to blame

# added exists check
perl -MData::Rmap=rmap_hash -le 'rmap_hash {print keys %{$_->{a}} if e
+xists $_->{a} } ({a=>{1,2}})'
1
[download]

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Re^3: Perl leve control of hash iterators by diotalevi (Canon) on Feb 28, 2007 at 04:25 UTC
Well... you'd probably better modify whatever you were given so it is read-only so the iterators can be reset and then you'd better do the reset/iterate-to-orig thing. Or... avoid ever using each() in Data::Rmap or take the "call arbitrary code" part out of Rmap or disallow using hashes. ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊	[reply]
Re^3: Perl leve control of hash iterators by bart (Canon) on Feb 28, 2007 at 11:27 UTC
`push @return, $self->_rmap($_) for values %$_;` [download] Hmm, if you do this another way, you must be able to avoid the problem: `push @return, map { $self->_rmap($_) } values %$_;` [download] Here, values is finished before the map even starts. However... you won't have a problem in the original unless the values is traversed lazily. You never know...	[reply] [d/l] [select]

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