From: Srijayanth Sridhar <srijayanth@...>
Date: 2009-03-26T20:27:36+09:00
Subject: Re: program design - template design pattern

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On Thu, Mar 26, 2009 at 4:23 PM, Robert Klemme
<shortcutter@googlemail.com>wrote:

> 2009/3/26 Srijayanth Sridhar <srijayanth@gmail.com>:
> > While a lot depends on several other aspects of your project, this
> specific
> > problem depends on a principle question:
> >
> > Do you have any control over the feed object?
>
> I second that.  Also, what type is "feed"?  That's not clear to me.
>
> > If you have any control, then you could make a polymorphic superclass
> called
> > Feed and go on from there where each separate feed has its own related
> > methods to deal with its idiosyncrasies and polymorphic methods that deal
> > with common tasks. For ex:
> >
> > class Feed
> >   def initialize
> >   end
> >   def parse_content
> >   end
>
> One could also add
>
>  # download the feed
>  def fetch(uri)
>     ....
>   end
>
> > end
> >
> > class BbcFeed < Feed
> >   def parse_content
> >      # do something relevant here
> >      # probably return a string/hash/or content object
> >   end
> >   # define other methods specific to BbcFeed etc
> > end
> >
> > Once this is done, you just have to create the right object at runtime,
> > perhaps have a factory object detailing this.
>
> Or stuff the relationship between feed URI's and class that deals with
> it in a Hash:
>
> FEEDS = {
>  'http://foo.bar/feed.rdf' => BbcFeed,
>  'http://baz.boz.buz/path.rdf' => BbcFeed,
>  'http://what.ever.you/like' => OtherFeed,
> }.freeze
>
> Then you can do
>
> FEEDS.each |uri, cl|
>  feed_handler = cl.new
>  feed_handler.fetch
>  feed_handler.parse_content
> end
>
> > If you don't have control, there isn't a way to run away from doing
> checks
> > on the object. Depending on how you determine the regex to use, you could
> > have specific solutions. Perhaps each feed has a different URL that you
> > could use to determine the parsing, or perhaps something else in the
> > xml...either way, you have to know what object you are dealing with, or
> you
> > have to write a parser that deals with it.
>
> Feed type checks could be done on the URI or the content.  Depending
> on that a different approach needs to be followed but the basic
> pattern stays the same.


Yeah I thought of that too, but God knows what his criterion for choosing
the parser are. It might be more complex than just a simple uri mapping.


Jayanth


>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
>
>

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