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The second one is not textually identical but if ${$x} = $y means the same thing as $x = \$y then I can't see what DD did wrong. Do they mean the same thing?

No. $x=\$y; makes $x's value be a reference to $y. $$x=$y makes the var referenced by $x to become a copy of the value in $y.

Think of what happens when you do $obj->[0]=1; With the first example [$x,$y] if we do so we see that ${$obj->[1]} does not change, with the second example we see it does. In the first example we are dealing with 6 items, an SV containing a ref to an array which contains two SVs which themselves contain refs to two more SV's which are self referential. In the second case we are only dealing with four items, an SV containing a ref to an array which two SV's which are self referential. Because of the way DD works these two cases appear to it to be identical.

Basically the problem is that it can't output a ref to a scalar that is itself part of a composite item being dumped later properly. It doesnt find out until way too late, and once it does, it doesnt do anything about it. If you start considering aliases then it gets things really wrong.

DDS avoids these problems by traversing the data structure twice using the refcounts to determine what it needs to keep an eye on (to avoid the problem you proposed to fix in DD) and uses that information later to ensure such things as this get handled properly. It also does the first pass in a breadth first fashion and then uses that info to control the later depth first output, which means that DDS dumps of self referential data tend not to look as crazy (ie a list of nodes of a tree structure doesnt result in the full tree being dumped from the first node, but rather evenly across the roots selected). The notation there is useful too: 'R: $ARRAY1->[1]', means "this scalar slot contains a reference to $ARRAY1->[1] but that the latter isnt defined yet". Likewise the 'V: $ARRAY1->[1]' means that "this scalar is a copy of the value of $ARRAY1->[1] but the latter isnt defined yet".

Incidentally one thing i regret is making the default to be Purity(1), i should have made it Purity(0) as well. :-(

use Data::Dumper; use Data::Dump::Streamer; $Data::Dumper::Purity=1; my ($x,$y); $x=\$y; $y=\$x; test([$x, $y]); my $ary=[]; $ary->[0]=\$ary->[1]; $ary->[1]=\$ary->[0]; test($ary); sub test { my $VAR1; my $s = shift; my $d = Dumper($s); my $s2 = eval "$d;\$VAR1"; $s->[0]=1; $s2->[0]=1; die $@ if $@; print "original---------------\n"; print Dump($s); print "DDed---------------\n"; print Dump($s2); print "\n" } __END__ original--------------- $ARRAY1 = [ 1, \\do { my $v = 'V: $ARRAY1->[1]' } ]; ${${$ARRAY1->[1]}} = $ARRAY1->[1]; DDed--------------- $ARRAY1 = [ 1, \\do { my $v = 'V: $ARRAY1->[1]' } ]; ${${$ARRAY1->[1]}} = $ARRAY1->[1]; original--------------- $ARRAY1 = [ 1, 'R: $ARRAY1->[0]' ]; $ARRAY1->[1] = \$ARRAY1->[0]; DDed--------------- $ARRAY1 = [ 1, \\do { my $v = 'V: $ARRAY1->[1]' } ]; ${${$ARRAY1->[1]}} = $ARRAY1->[1];

Cheers

---
demerphq


In reply to Re^7: In need of a Dumper that has no pretentions to being anything else. by demerphq
in thread In need of a Dumper that has no pretentions to being anything else. by BrowserUk

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