Eily asked in the CB, here the answer: *

Basically:

• each has no problem if you delete the current element
• if you delete other elements, you need to reset the iterator, e.g. with keys
• then the iterator starts anew with the remaining elements
• NB if you don't empty the whole hash, you risk an endless loop.

The following demo is always resetting, but doesn't need to.

 
  DB<41> @h{a..c,A..C} = (1..3,11..13)

  DB<42> x \%h
0  HASH(0x33bf940)
   'A' => 11
   'B' => 12
   'C' => 13
   'a' => 1
   'b' => 2
   'c' => 3
  DB<43> while (my ($k,$v) = each %h ) { delete $h{$k}; print "$k,$v\n
+"; delete $h{uc($k)} } continue {keys %h }
c,3
a,1
B,12
b,2
[download]

Question to follow ;-P

UPDATE

*) this was a root post which was re-parented to the later question. Partly because it toook eily more than 15 min to ask, but mainly because I liked the idea to defy causality! ;-)

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