Re: How Are Attributes Useful?

[chromatic]

I've used attributes productively a few times.

In a client server application, I used attributes on methods of the model classes to implement access controls. The syntax was something like :Access( rw ) to mark a method as needing read and write access. The actual server class performed authorization and authentication and knew the permissions of remote users. Before delegating any method call to a model object, it would check the permissions.

I could have done this without attributes, but it seemed like a nice way to keep the metadata (what does this method accomplish) in the same place as the actual code of the method.

In a recent journal entry (Dark, Dark Corners of Perl), I speculated that it's possible to use attributes on methods to simplify declaring and accessing parameters. I'm not ready to demonstrate my proof of concept yet, but I really like how the syntax works. It's nice to be able to manipulate subroutines at the appropriate time without resorting to source filters.

[Ovid]

chromatic wrote:

In a recent journal entry (Dark, Dark Corners of Perl), I speculated that it's possible to use attributes on methods to simplify declaring and accessing parameters. I'm not ready to demonstrate my proof of concept yet, but I really like how the syntax works. It's nice to be able to manipulate subroutines at the appropriate time without resorting to source filters.

I wholeheartedly agree, and between the two, I would use your solution over mine any day of the week if it's feasible, but I have a couple of questions. First, can you do multi-method dispatch with that? I've been porting some Java to Perl and lack of MMD has been a pernicious source of bugs.

Second, will this run under mod_perl? It's my understand that attributes rely on a CHECK block. That won't get triggered under mod_perl. I know we discussed this the other day, but for the life of me, I can't recall what was said :)

[chromatic]

I think it'd be very easy to do MMD with this technique. There's one potentially tricky spot, but I think it's doable.

I also think attributes will run just fine under mod_perl. Maypole uses them, for example, and it works. There are different ways to declare where Attribute::Handlers runs, for example.

[perrin]

I don't use attributes, so I can't vouch for it either way, but if they don't work under mod_perl, someone should tell the Maypole developers that. It uses sub attributes for security purposes.