I would say they are more like "include" in Ruby. With Java  
interfaces, you still need to code the implementation of the methods,  
whereas with Traits, you are incorporating the functionality of those  
methods. Sort of like "including" a library of methods.

- Daniel

On Sep 3, 2005, at 1:50 PM, Eric Goebelbecker wrote:

> So, at the risk of oversimplifying, are traits very similar to
> interfaces in Java?
>
> On 9/3/05, Tom Phoenix <rootbeer at redcat.com> wrote:
>
>> On 9/3/05, Alan Grimes <alangrimes at starpower.net> wrote:
>>
>>
>>> The first issue is that I have hardly a clue as to what is meant  
>>> by a
>>> "trait". It was never mentioned in any of the classes I took or  
>>> in any
>>> of the textbooks I have read on my own time.
>>>
>>
>> They're a relatively new concept in Smalltalk. The general idea (and
>> somebody correct me if I'm wrong) is that a trait can become an
>> ancestor to a class without being a class itself. That is, a trait is
>> a dictionary of related methods; you may use most or all of those
>> methods without further modification in programming a class.
>>
>> For a real-world-ish example, if I were making an Automobile  
>> object, I
>> would need to include methods to allow a key to open or start the
>> Automobile. Similarly, if I were making an Apartment or a Locker, I
>> would need methods to allow a key. But instead of making all of those
>> inherit from LockableObject, I could have a trait for Lockability.  
>> Any
>> object with that trait has methods understanding, say, that the wrong
>> key doesn't work in the lock.
>>
>> So, why not make all of those inherit from LockableObject? Because  
>> the
>> Automobile inherits from Vehicle, which may or not be a
>> LockableObject. The others don't have lockable ancestors either. We
>> don't want to make all of the ancestor classes lockable, and we don't
>> want to duplicate the lockability code in each of the classes that
>> needs it.
>>
>> In other words, when traits are available, you may inherit some
>> methods from ancestor classes, and some from ancestor traits. The
>> traits allow you to share ancestor methods without having to have a
>> common ancestor with those methods.
>>
>> Hope this helps!
>>
>> --Tom Phoenix
>>
>>
>>
>
>
> -- 
> Back when I was a boy, we carved our own IC's out of wood.
>
> Eric Goebelbecker
> eric at ominor.net
> http://eric.ominor.net
>
>