Hi Judah,
X10 does not support declaration site variance.
String implements Comparable[String], Int implements Comparable[Int] etc.,
but neither Comparable[String] nor Comparable[Int] are subtype of
Comparable[Any] thus "abc" as Comparable[Any] does not work in X10. There
is no way to implement what you want in pure X10.
If your target is managed X10 only, you can write a static method in Java
that takes r:Any/*Rail[Comparable[Any]]*/, i:Int and
o:Any/*Comparable[something]*/, whose body is something like
"((x10.core.Rail)r).getObjectArray()[i] = o;", then call it from your X10
code.
-- Mikio
2013/8/21 Judah Diament <dju...@us.ibm.com>
> in our case the desire is to know absolutely nothing about the type
> parameter.
>
>
> Thanks,
> Judah Diament
> IBM T.J. Watson Research Center
> P.O. Box 704 Yorktown Heights, NY 10598, USA
> 914-784-7813 (TL: 863)
>
> "Successful innovators use both the right and left sides of their brains.
> They look at figures. They look at people. They work out analytically what
> the innovation has to be to satisfy an opportunity. Then they go out and
> look at potential users to study their expectations, their values, and
> their needs."
> *-Peter F. Drucker*
>
>
>
> From: David P Grove/Watson/IBM@IBMUS
> To: Mailing list for users of the X10 programming language <
> x10-users@lists.sourceforge.net>,
> Date: 08/19/2013 06:18 PM
> Subject: Re: [X10-users] a Rail of comparables
> ------------------------------
>
>
>
> Judah Diament/Watson/IBM@IBMUS wrote on 08/19/2013 04:16:56 PM:
> >
> > Is there a way to create a Rail whose type is java.lang.Comparable
> > (which is an interface), as in
> >
> > import java.lang.Comparable;
> > ...
> > val myRail: Rail[Comparable];
> >
> > where I don't know what the actual class of the instances passed in
> > from Java code for myRail to hold will be, but I also don't care
> > because all I want is to be able to use the compareTo() method?
> >
> >
>
> Hi Judah,
>
> In both Java and X10 Comparable is actually Comparable[T] (ie, a generic
> interface with one type parameter). Since Java erases generics it lets you
> ignore that sometimes. X10 doesn't erase generics, so it is going to
> insist that you say Comparable[SOME_TYPE] not just Comparable.
>
>
> Do you really know nothing about the type parameter of the Comparable, or
> will something like the stubbed out code below work for your usage?
>
> --dave
>
>
>
> abstract class A implements Comparable[A] {
> public abstract def compareTo(A):int;
> }
>
> interface I extends Comparable[I] {
> public def compareTo(I):int;
> }
>
> public class Test {
> public static def main(args:Rail[String]) {
> val r = new Rail[Comparable[A]](10);
> val r2 = new Rail[Comparable[I]](10);
> }
>
> static def test(x:Rail[Comparable[A]], y:A) {
> return x(1).compareTo(y);
> }
>
> static def test2(x:Rail[Comparable[I]], y:I) {
> return x(1).compareTo(y);
> }
>
> }
>
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