[Newbies] Re: Traits (Was Design best practice : put state-independentmethodsonclass side?)

itsme213 itsme213 at hotmail.com
Thu Mar 27 15:13:47 UTC 2008

I compare a trait to a superclass, in that it can provide implemented 
methods, and require (i.e. like template method hooks or callbacks) other 
"expected" methods in the class that uses that trait e.g. any state a trait 
expects would have some expected accessors.

In your example you could use PetTraits with any class that implemented 
#foodRequirements, not just Dog or Rock subclasses.

You can also re-name (actually, alias) provided methods when you use a 
trait; you cannot (currently) re-name the required methods which is often 
useful http://www.nabble.com/A-Traits-question-td15484148.html#a15600165 and 
I would use them a lot more if I could do this kind of re-naming.

- Sophie

"Rob Rothwell" <r.j.rothwell at gmail.com> wrote in message 
news:22f158f00803251855h3f9e1bbenf370cb5c4b2bffbc at mail.gmail.com...
> On Tue, Mar 25, 2008 at 8:02 PM, Matthew Fulmer <tapplek at gmail.com> wrote:
>> No. Traits are units of behavior that can be shared among
>> objects.
> So...if in a general sense a trait has no knowledge of the object it will 
> be
> attached to, is it common practice to create traits to be used only by a
> specific group of objects so that some common behaviour can be assumed?
> Or at that point are you just creating a subclass and should just go ahead
> and duplicate the methods?
> As a trivial example, say you have Dog and Rock, and you want to make a 
> Pet
> out of both of them even though they both have different base classes 
> (like
> Animal or Mineral).  Furthermore, Pet>>careInstructions needs to use "self
> foodRequirements," which you may provide for a Dog or a Rock, but not for
> all objects.
> In other words, would you expect to see PetTraits that are meant to be 
> used
> with Dog or Rock subclasses only?
> Thanks!
> Rob


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