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Re: Let a module call a sub of the caller

by sundialsvc4 (Abbot)
on Sep 06, 2012 at 22:44 UTC ( #992201=note: print w/replies, xml ) Need Help??


in reply to Let a module call a sub of the caller

This is an excellent application for what is known in computer-science circles as a closure.   Which Perl supports very well.

You can, within a subroutine, define a variable to be a “code reference,” that is to say, to a particular sub that you define on-the-spot and which can refer to local variables or anything else that is “visible” at the particular place where you define that sub.  

Your caller should simply define one of those closures, and pass it in as a parameter to the routine, who simply calls it.   The closure will execute in the context of the code that created it ... that is to say, “your caller.”

“It’s slick to the point of being positively elegant,” and it works.   (May I kindly refer you to a plethora of existing docs here and elsewhere on the Internet for the gory procedural details.)

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[Corion]: ... or so I think. As I said, I'm somewhat vague on how to make AnyEvent cooperate with a callback-driven IO event loop that gives me callbacks when data is available or can be written
[ambrus]: what push_write thing? I don't think you need that. that's implemented generically by AnyEvent::Handle
[Corion]: ambrus: Yeah, that's what I think as well. But you give me an idea, maybe I should start with implementing the timer, as that should be far simpler and with fewer edge-cases/nasty interaction than the file watcher
[ambrus]: You only provide the watcher part that tells when the handle is readable or writable, not the actual writing and reading.
[Corion]: ambrus: Hmmm. It makes sense that AnyEvent would implement the push_write itself, but I think I don't have a good idea of where the boundary between AnyEvent and the underlying event system lies... Implementing the timer should give me a better idea
[ambrus]: Corion: push_write is in the higher level abstraction of AnyEvent::Handle, not in the watcher
[Corion]: ambrus: Hmm - rereading Prima::File, that merrily coincides with what Prima does - it tells you "you can read", and you're supposed to read from the fh yourself. I thought it called you with the data already read, which would've been harder to integrate
[ambrus]: you just need an io watcher, created by &AnyEvent::Impl:: Whatever::io(...)
[Corion]: So after talking it through with you even while I'm still not entirely clear on where AE ends and my implementation begins, I think I understand that I only need to implement some smaller parts for each functionality I want to support.
[Corion]: Yeah... and you might even be able to mix and match additional functionality if you have additional async suppliers, like from a separate thread

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