Re: [scala] Constructor parameters for traits

> But what about this?:
>
> trait Base{ val msg: String }
> trait Sub1 extends Base{ override val msg = "hello" }
> trait Sub2 extends Base{ override val msg = "goodbye" }
> Object Test extends Sub1 with Sub2
>
> The above code works fine. Why not apply the same rules to solve
> diamond inheritance?
>
> - Andrés
>
> 2008/12/2 James Iry <jamesiry@...>:
>> Diamond inheritance creates extra complexity.  Here's one example
>>
>> trait Base(val msg : String}
>> trait Sub1 extends Base("hello")
>> trait Sub2 extends Base("goodbye")
>> Object Test extends Sub1 with Sub2
>> println(Test.msg) // hello?  goodbye? error?
>>
>> There are ways for a language to let you resolve diamond inheritance.  But
>> it does complicate things.
>>
>> On Tue, Dec 2, 2008 at 9:17 AM, Sebastien Braun <sebb@...>
>> wrote:
>>>
>>> Hello, List.
>>>
>>> I know that traits can not have constructor parameters, however I have not
>>> been able to find out much about the rationale behind this restriction; my
>>> google-fu fails me and the SLS is quiet on it (or, maybe, I just don't
>>> know
>>> where to look for it).
>>>
>>> For this scala code
>>>
>>> > trait A {
>>> >   System.out.println("Hello, World!")
>>> > }
>>> >
>>> > class AImpl extends A
>>>
>>> scalac will generate (something closely resembling) the following
>>> pseudo-Java:
>>>
>>> > public interface A {}
>>> >
>>> > public class A$class {
>>> >       public static void $init$(A $this) {
>>> >               System.out.println("Hello, World!");
>>> >       }
>>> > }
>>> >
>>> > public class AImpl implements A {
>>> >       public A() {
>>> >               A$class.$init$(this);
>>> >       }
>>> > }
>>>
>>> So, intuitively (and perhaps naïvely...), it seems to me that the compiler
>>> should also be able to accept constructor parameters for traits:
>>>
>>> > trait A(message: String) {
>>> >       System.out.println(message)
>>> > }
>>>
>>> and just tack on the arguments to the $init$ method of the trait's
>>> implementation class:
>>>
>>> > public interface A {}
>>> >
>>> > public class A$class {
>>> >       public static void $init$(A $this, String message) {
>>> >               System.out.println(message);
>>> >       }
>>> > }
>>>
>>> Is this a bad idea?
>>>
>>> Cheers,
>>>
>>> Sébastien
>>
>>
>