Extension methods vs. Traits

[Alex Blewitt]

Traits also suffer in Scala, because when the implementation of a  
trait changes (such as bugfixing a method), the compiler has to be re- 
run over all sources that use that trait. It's one of Scala's biggest  
weaknesses that it is essentially a source-only compiled language.

Please don't lets follow the route of other lambda proposals and make  
this more than it should be - but leave traits to a separate  
implementation.

Alex

On 11 Dec 2009, at 09:45, Daniel Latrémolière wrote:

> I would like to understand the final paragraph of the proposal where  
> you are saying that the traits are much more significant change than  
> extension methods to the language and VM.
>
> The VM doesn't need to implements traits. The compiler can transform  
> one trait in one interface with abstract methods and declaration- 
> sites for non-abstract methods and one anonymous class with the non- 
> abstract methods coming from the trait and referenced in the  
> interface by declaration-sites.
> Then I don't think traits are a bigger change in VM than extension  
> methods, because this can be only a language feature implemented by  
> compiler using your declaration-site in bytecode.
>
> For the language, I think traits are much more readable, because  
> code is local, and doesn't not ask to follow the delegate to the  
> static method in another class file. I think traits are reusing much  
> more current Java language (method syntax) and doesn't introduce a  
> new construct like declaration-site extension methods. But, I have  
> not studied all possible effects in Java language.
>
> Thanks for the explanations,
> Daniel Latrémolière.
>
>