my $param = shift;
    ...
    $self->{$_call} = $_param || return $self->{$_call};
[download]

I assume $param and $_param were supposed to be the same. That's a little obfuscated, and doesn't allow setting parameters to false values. A more typical way to do it is:

    # (after shifting everything but param)
    if (@_) {
        return $self->{$_call} = shift;
    } else {
        return $self->{$_call};
    }
[download]