in reply to Re: optimization - exists should return a reference
in thread optimization - exists should return a reference

Surely 

exists $_->{$client} and return $_->{$client}
   for $export_def->{'..client_default_version'};

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Would just become 

return $$_ if $_ = exists $export_def{'..client_default_version'}{$cli
+ent};

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Which gives the desired once-and-once-only behaviour?

Examine what is said, not who speaks.

The 7th Rule of perl club is -- pearl clubs are easily damaged. Use a diamond club instead.

In Section Meditations