Re^5: multiple values for one key in hash

How would autovivification know that the undef in lvalue context it's autovivifying wasn't the original undef?

$ perl -MYAML::Syck -le '$h{bar}=1;$h{bar}=undef;push @{$h{bar}}, qw/a
+ b c/;print Dump( \%h )'
--- 
bar: 
  - a
  - b
  - c
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The cake is a lie.
The cake is a lie.
The cake is a lie.

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Re^6: multiple values for one key in hash by moritz (Cardinal) on May 13, 2008 at 14:51 UTC
How would autovivification know that the undef in lvalue context it's autovivifying wasn't the original undef? By using a proxy object that acts as undef. Note that you need a reference for autovivification anyway because `push @{...}` has to modify something that is stored in place of `...` anyway. I don't know if Perl 5 does it that way, but I think kp6 does.	[reply] [d/l] [select]
Re^6: multiple values for one key in hash by dragonchild (Archbishop) on May 13, 2008 at 14:12 UTC
huh. My understanding was always that an exists check was done in the background (reflecting my experience with the tied madness that is DBM::Deep), but I've never felt curious enough to explore more deeply. My criteria for good software: Does it work? Can someone else come in, make a change, and be reasonably certain no bugs were introduced?	[reply]