Doesn’t such a method make the behavior of a programming language unpredictable?

Not if perl is sure that the situation allows optimizing out.

I would blindly assume that all returns could be optimized out in this script:

sub foo
{
    # do something
    return;
}

sub bar
{
    # do something
    return 'a scalar';
}

sub baz
{
    # do something
    return qw( a list );
}

foo();
bar();
baz();
exit();
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Alexander