OO vs. procedural style

[markjugg]

Thanks ncw. I had thought of an arrangement like the one above. I think the code design could be considered to cleaner, but here's what bothers me about it:

One programming principle is "optimizing for the common case". The common case here is that I create a new "err" call in a script, as above. If I switch the OO style, instead of writing out 'err' each time, I'm now writing out '$err->err', so the solution makes more work in the common case.

What about the magic that CGI.pm uses, where you can call routines with an OO style, or with a procedural style, and you don't even have to start with "new CGI", because there's a default object created. Can someone explain that?

As far as fetching the caller's package, perl makes that easy: $callers_pkg = caller;

I did end up using that in an inbetween module once, with the logic of "If my caller's package has defaults use those, otherwise use the defaults in CGI::Err". It worked, but that didn't seem clean either...

Thanks for any further comment. -mark

[tilly]

The trick that CGI uses is all in the following sub:

sub self_or_default {
    return @_ if defined($_[0]) && (!ref($_[0])) &&($_[0] eq 'CGI');
    unless (defined($_[0]) && 
            (ref($_[0]) eq 'CGI' || UNIVERSAL::isa($_[0],'CGI'))
                 # slightly optimized for common case
            ) {
        $Q = $CGI::DefaultClass->new unless defined($Q);
        unshift(@_,$Q);
    }
    return @_;
}

They preprocess the args to every function this way, and as long as the first arg is 'CGI' or an object that inherits from CGI they leave the arguments alone. Otherwise they prepend a global to the list.

This is nice but imposes quite a bit of overhead.

Another way of doing the same thing is to make the procedural interface be in a different package, and have a well thought-out AUTOLOAD sub that creates needed procedural wrappers at run-time. More complex but probably more efficient than what CGI does.

Another solution that I have used is to think functionally. There you actually have your error handler be an anon sub. By default it is your default, but it can be anything you want. In this case you would leave your package alone and in your CGI script say:

$handler ||= \&Err::err;
# time passes
do_the_right_thing() || $handler->(title=>'Oops',msg=>'something went 
+wrong');

If $handler is left alone, well you get the default. But anyone who wants can change it.

I have often found that this functional approach is a more efficient way to implement optional hooks. YMMV.