[SOLVED] Subtle Q: what does 'Apache2::RequestRec' return for missing "param()"?

locked_user sundialsvc4 has asked for the wisdom of the Perl Monks concerning the following question:

Edit: I fixed it.

I have, as you know, a legacy app that used mod_perl and therefore a Apache2::RequestRec and a Apache2::Request.

Exactly what did that module return for my $scalar = $request->param('foo'); if 'foo' did not exist? Was it undef, or was it an empty string? The reason I ask, is that the original code apparently assumed empty-string.

(Large amounts of whining deleted...)

The problem here is that param is a very complicated function. It can be called with zero parameters or one, and in an array context or a scalar context. The existing code simply did this:

has 'plack_request' ... handles param => 'param', ...

... and it Just Works.™

(More whimpering deleted ...)

Thanks to the clue given in post 853728, I solved the problem, I think:

around 'param' => sub {
    my $orig = shift;
    my $self = shift;
    
    my @result = $self->$orig(@_);

    if (wantarray) {
        return @result;
    }
    else {
        return defined($result[0]) ? $result[0] : '';
    }
};
[download]

Replies are listed 'Best First'.
Re: [SOLVED] Subtle Q: what does 'Apache2::RequestRec' return for missing "param()"? by ikegami (Patriarch) on Jun 08, 2011 at 18:15 UTC
`handles => { param => 'param', },` [download] is effectively `handles => { param => sub { my $plack_request = shift->plack_request; return $pack_request->param(@_); }, },` [download] So instead of using `around`, you could use `handles => { param => sub { my $plack_request = shift->plack_request; return (wantarray ? $plack_request->param(@_) : $plack_request->param(@_) // '' ); }, },` [download] One less layers of subs, and less action at a distance.	[reply] [d/l] [select]
Re: [SOLVED] Subtle Q: what does 'Apache2::RequestRec' return for missing "param()"? by locked_user sundialsvc4 (Abbot) on Jun 08, 2011 at 21:48 UTC
Excellent! Thank you! ~~(Assuming `"\|\|"` for your `"//"`.)~~ `perldoc perlop` Needs Perl 5.10 though. After initial effusion, I wound up keeping `after` because it can be applied to a `qw()` list of attributes which leverages just one bit of code for all of them.