Your problem comes from the combination of the my ... with the defined-or operator. It's an operator precedence issue: put (my ...) in brackets. You can also use the low-precedence or operator, but only if you can guarantee that 0 will never be a valid return.

sub context { wantarray ? (qw/foo bar/) : -1 }

my ($not_foo) = context() // say "Whoops";
say $not_foo;

(my ($foo) = context()) // say "Whoops";
say $foo;

# This works if context() can never return 0
my ($also_foo) = context() or say "Whoops";
say $also_foo;

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In reply to Re: Odd (to me) case of wrongly guessing context by rjt
in thread Odd (to me) case of wrongly guessing context by ibm1620

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