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Re^3: Real life uses for closures.

by runrig (Abbot)
on Feb 13, 2013 at 00:36 UTC ( #1018470=note: print w/replies, xml ) Need Help??


in reply to Re^2: Real life uses for closures.
in thread Real life uses for closures.

Heh, reading that link, one of the basic things I've used closures for lately is filtering a list in different ways. I had one utility function that goes into a loop parsing email files from a directory (and if successful, finally returning the attachments from the one you want according to some parameters) and skipping files that it's already seen before. Then I found that in some particular case I needed to call the function multiple times and have it remember what it had seen from the previous call. So I turned the filtering function into a parameter, allowing you to maintain the hash of 'seen' email files outside of the loop in the main function (but keeping the original behaviour by default, which is what I want most of the time). Pretty basic example...but there it is.

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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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