!1 returns Perl's "false" value. You can get the same effect via:

sub false {
    my $f= "";
    {
        BEGIN {
            warnings->unimport()   if  $INC{"warnings.pm"};
        }
        local( $^W )= 0;
        my $temp= 0+$f;
    }
    return $f;
}
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That is, the "false" value simply has a string value of "" and a numeric value of 0. Thus there is no warning when in numeric context since the 0 is simply fetched rather that it having to be computed from the empty string.

        - tye