in reply to Perl Hash Behavior.

> efficient way to check if a value exists in a hash, and if not, assign 0

golfing 

  DB<105> %h=(); print $h{key} //= 0;
0
  DB<106> \%h
 => { key => 0 }

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Update: beware that like this values like undef are not allowed!

Otherwise better use exists

Cheers Rolf

( addicted to the Perl Programming Language)

In Section Seekers of Perl Wisdom