The following is mostly an educated guess, as I have not actually grokked the guts first hand.

It seems that both of these effects hinge on the duality of my having effects both at compile as well as runtime. Sprinkle a couple BEGIN { AttrTest->dump_lex('begin(1)') } in there and it becomes obvious that the pad gets fully populated during compilation, with all variables ever associated with the current pad being visible regardless of scope. In contrast, at runtime, the pad only contains those variables which are in scope - in fact, a variable doesn't appear in the pad before the entire statement during which it is declared has executed. It's for that reason that you can write my $x = 10; { my $x = $x; print $x } and get 10.

End educated guess.

Now with that, on to address each piece of the puzzle:

  1. INIT blocks are called after compilation has succeeded but before it is terminated. Therefor, they can see everything that's ever going to be in the pad they're associated with.
  2. In 5.6 the implicitly called MODIFY_HASH_ATTRIBUTES can see %foo because it is called during INIT - so the same rules as above apply.
  3. In 5.8 it can't, because the statement has not yet fully executed so the entry on the pad is not there yet.
  4. You're invoking the last dump_lex at runtime, outside the scope of either hash, so neither of them is visible in the pad.
I may well be wrong, but that picture seems to be seamless.

Makeshifts last the longest.

In reply to Re: Lexical pad / attribute confusion by Aristotle
in thread Lexical pad / attribute confusion by adrianh

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