Re: [scala] Constructor parameters for traits

> 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
>
>