I think my(EXPR?$x:$y) = 3; is equivalent to: 
my $x = 3 if EXPR;
my $y = 3 if !EXPR;

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which is a known issue, and may do unexpected things if EXPR is false (although there has been code out there that (mis)uses this). Since 5.10 there has been a warning on 
my $x if EXPR;

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is EXPR can be determined to be false at compile time (constant folded to 0).

I wouldn't worry about my(0?$x:$y) too much. It's not something people will be do by accident - it isn't documented to work, so people who do it shouldn't be surprised if their code no longer works after upgrading Perl.

In reply to Re: my (0?$a:$b): a koan by JavaFan
in thread my (0?$a:$b): a koan by educated_foo

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