Altering the Return Value: Postwrappers

• The postwrapper can see the function's original return value

• This is quite simple:

        $return = &$original;
        $dummy = scalar $wrapper{post}->(@_, $return)
                if $wrapper{post};

• Altering the return value is simple, but subtle:

        return $return;

• Variables in Perl function calls are aliased inside the called function

        sub set_to_57 { $_[0] = 57 }
        my $x = 119;
        set_to_57($x);
        print "$x\n";           # prints 57!!

• Assigning to $_[-1] inside of the postwrapper modifies $return!

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Copyright © 2003 M. J. Dominus