[Baypiggies] Trivial OOP pattern problem

Shannon -jj Behrens jjinux at gmail.com
Sat Jun 16 02:56:26 CEST 2012

(Slightly off topic.)

I am a language guy, so I love looking at other languages for cool
features.  You're looking for a way to chain a bunch of method calls
together, a la jQuery.  It turns out that Dart recently added a feature
called method cascades that solve this problem:



I'm not encouraging you to switch to Dart; I just think it's interesting.


On Thu, Jun 14, 2012 at 9:53 PM, Ian Zimmerman <itz at buug.org> wrote:

> I am writing some code using the cairo drawing library, or rather the
> pycairo binding to it.  Unfortunately I sense a bit of API misdesign
> with the binding.  To draw into a context ctx which I obtained somewhat
> like this:
> import cairo as C
> ctx = C.Context(surface)
> I am supposed to write a series of calls like this:
> ctx.set_source_rgb(1.0, 1.0, 1.0)
> ctx.rectangle(0.0, 0.0, float(rw), float(rh))
> ctx.fill()
> ctx.scale(sx, sy)
> ... and it piles up.  Each of these methods returns None, whilst it
> should conceivably return self, adding a lot of convenience:
> ctx.set_source_rgb(1.0, 1.0, 1.0).rectangle(0.0, 0.0, float(rw),
> float(rh)).fill()
> I would like to write a wrapper class around Context to enable this
> usage, but I don't know how to do that sanely.  Sure, I could do this:
> class ContextWrapper(object):
>      def __init__(self, surface):
>          self.ctx = C.Context(surface)
>      def fill(self):
>          self.ctx.fill()
>          return self
>      def scale(self, sx, sy):
>          self.ctx.scale(sx, sy)
>          return self
>          ...
> but then I have to wrap each method explicitly, or at least each method
> I use.  I don't consider that sane.
> Is there a trick I am missing, perhaps using __dict__ or __getattr__ by
> which I could wrap all the methods wholesale?
> --
> Ian Zimmerman
> gpg public key: 1024D/C6FF61AD
> fingerprint: 66DC D68F 5C1B 4D71 2EE5  BD03 8A00 786C C6FF 61AD
> http://www.gravatar.com/avatar/c66875cda51109f76c6312f4d4743d1e.png
> Rule 420: All persons more than eight miles high to leave the court.
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