Isn't this because the precedence makes it: 

$x = undef;
my $a=($x // warn 'RHS evaluated'); 
say $a;

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Since $x is not defined, // returns the right hand side, and the call to warn returns 1 (true) to report success.

Aaron B.
My Woefully Neglected Blog, where I occasionally mention Perl.

In reply to Re^4: Perl5 Language Extension: Definedness-Triggered Shortcut Operators by aaron_baugher
in thread RFC: Perl5 Language Extension: Definedness-Triggered Shortcut Operators by martin

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