[BangPypers] returning value from a class

[Noufal Ibrahim]

On Wed, Apr 06 2011, Sidu Ponnappa wrote:

>> Why do you want to create a class that doesn't create itself when called?
> It's interesting this came up today - we were just arguing about this
> at work on Monday. Some of my colleagues are of the opinion that this
> is a Bad Thing and should never be done. I agree that while it's a bad
> thing, there are rare occasions where it's still the most elegant
> solution. After all, the allocator is just a factory - I don't see why
> it should be treated as something special. As long as you have some
> rules (like the rules for overriding the default equality method in
> any OO language) you should be fine.

Yup. It is a factory and seeing it that way makes things
clearer. However, it's one of those things that comes after messing with
stuff for a while rather than something taught.


> FWIW, these are my two rules:
> * Don't do it unless there's no other sensible option. Like, absolutely
> nothing else exists that is more elegant.

I'm not "against" it. Overriding the __new__ method in python (i.e. the
allocator) is often done while metaclassing to create speciallised
objects. e.g. with custom accessors and stuff like that. 

However, like you said, it's a rule to be broken only when you know what
you're doing. 

> * Ensure that you're returning a sub-class of the class where you're
> implementing a custom allocator. No returning a different type, and
> definitely no returning a nil.

This makes sense. Liskov's principle would be honoured and things would
be more predictable.

> Here's one occasion where I had call to do this. See
>
> https://github.com/kaiwren/wrest/blob/master/spec/wrest/native/response_spec.rb#L41
>
> for the spec and
>
> https://github.com/kaiwren/wrest/blob/master/lib/wrest/native/response.rb#L43
>
> for the code. It's in Ruby, though.

So you'll actually build a redirection instead of just a response for
the 3xx status codes? 

I don't know Wrest and the rest of the code well enough to have an
opinion on being right or wrong but it does illustrate your point
though. 

[...]



--