Parameters for object callback

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

I've whipped up a OO system, and I have a way for the user to provide callbacks (many different ways, but anyway...). What parameters, and in what order, are the most convenient for users?

I've written an app using my toolkit, and at the moment, the order is:

The value the user entered for this object
A reference to the object that the callback belongs to
A reference to the top of the object tree
A reference to a hash of all the name=>value pairs for all the objects that have had parameters altered (so the user can spy on other objects).

Can anyone suggest things that I'm missing, or what would be more convenient?

____________________
Jeremy
I didn't believe in evil until I dated it.

Comment on Parameters for object callback

Replies are listed 'Best First'.
•Re: Parameters for object callback by merlyn (Sage) on Nov 06, 2002 at 04:39 UTC
Take a look at how HTML::Parser defines callbacks. Basically, you create a callback specifying a simple text string giving what you want in the callback. If your library builds a closure based on the user-supplied string, it could be quite fast. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re: Parameters for object callback by jdporter (Paladin) on Nov 06, 2002 at 03:50 UTC
With such a complex interface, it's hard to imagine any argument order being any better than any other. That said, the one criterion that one ought to keep in mind when deciding on argument order is: What arguments might reasonably be omitted? The one argument that could be omitted should be the last one. The two arguments that could be omitted should be the last two. And so on.	[reply]
Re: Re: Parameters for object callback by jepri (Parson) on Nov 06, 2002 at 04:05 UTC
I was trying to think of how my users might use it, but realistically I'm not going to be able to. So I guess its onto user testing and see what they say Thanks. ____________________ Jeremy I didn't believe in evil until I dated it.	[reply]
Re: Parameters for object callback by jdporter (Paladin) on Nov 06, 2002 at 14:07 UTC
Another possibility to consider is named arguments. Perl supports this easily by having your sub construe the argument list as "hash-like". That is, instead of `my @args = @_;` you could say `my %args = @_;` Then the caller could do something like `func( value => $obj_value, object => $obj, top => $top_node, affected_objects => { .... }, );` [download] With this scheme, it is easy to have any arguments be optional, rather than having to rank their "optionalness" as in the scheme I suggested above.	[reply] [d/l] [select]