in reply to Dereference anonymous AoA
Foreach loop provides list context, so foreach my $i ( @{ $aref } ) explodes into its elements
Here the first lines out error output:foreach my $i( ['kept', 82], ['notkept', 1], ['repaired', 3] ) { ... # so $aref->[$i][0] # looks like $areg->[ ['kept', 82] ][0] #
Now, why does it keep looping?$ perl buggy_array.pl 2> out.txt (it hangs here, press Ctrl-C to stop) $ head -6 out.txt Use of reference "ARRAY(0x1cfb148)" as array index at ary.pl line 21. Use of uninitialized value in concatenation (.) or string at ary.pl li +ne 21. Use of reference "ARRAY(0x1d0fad8)" as array index at ary.pl line 21. Use of uninitialized value in concatenation (.) or string at ary.pl li +ne 21. Use of reference "ARRAY(0x1d0fbf8)" as array index at ary.pl line 21. Use of uninitialized value in concatenation (.) or string at ary.pl li +ne 21.
19468616 is the memory address of $aref here. Which meansperl -E 'my $aref=[undef]; say 0 + $aref' 19468616
When you do stuff like $aref->[999][0] and element 999 of $aref doesn't exist, Perl will extend $aref. It will fill it with undef, up to element 999.$areg->[ ['kept', 82] ][0] # becomes something like # $areg->[ 9999999 ][0] # (or whatever the memory address of that array is...)
They call it 'autovivification' (sp?). (but if you do $aref->[999][500], Perl will not create the rightmost array - the one with 500 elements)perl -E 'my $aref=[undef]; $aref->[1000][0]; say scalar @{ $aref }' 1001
So, now your $aref has tons of of undefs. So the loop keeps looping and issuing warnings.
So yeah, all in all, that was a pretty interesting question, I must say.
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