Hello, Thank you for your answer, I appreciate!
Indeed, it is clear to me that if the feature should be a concern of both String and Stream (or more?), a common contract can be designed. The impl. you sketch is the more natural one I think. (it's also the one I gave in the other mailing grap about that toList stuff, so I guess it's ok!) I am just a bit cold about the idea that the spec will make the compiler's job, but I guess in Java there is no work around. I don't know what the community thinks about it. Regards, Justin Dekeyser On Wednesday, November 4, 2020, Rob Spoor <open...@icemanx.nl> wrote: > On 04/11/2020 14:18, Justin Dekeyser wrote: > >> Hello everyone, >> >> I have been following this mailing list for several months, and >> earlier today my attention was drawn to >> https://bugs.openjdk.java.net/browse/JDK-8140283. Actually I've been >> dreaming of such a feature for a long time now. >> >> I would really be interested in solving it, but I do not know its >> current state nor if someone would agree to sponsor my work on that. >> >> It would be my very first intervention in the Java code base. >> (Still have to make sure the Oracle agreement paper does not conflict >> with my current job contract, so nothing's ready for now.) >> >> Thank you for your time, >> >> Best regards, >> >> Justin Dekeyser >> >> > I'd like this feature as well, but why stop at Stream? String already has > the transform method, but StringBuilder (and StringBuffer) could also use > it. > > And that's where you're likely to start copy pasting. I've done so for > several builder classes I've written for myself. So here's a thought: why > add this method to classes, when you can create a trait using an interface > with a default method? > > public interface Transformable<T> { > > default <R> R transform(Function<? super T, ? extends R> f) { > // note: this would need documentation that a class X is > // only allowed to implement Transformable<X> > return f.apply((T) this); > } > } > > So you could get the following, and each would automatically get the > transform method: > * public class String implements Transformable<String> > * public class StringBuilder implements Transformable<StringBuilder> > * public class StringBuffer implements Transformable<StringBuffer> > * public interface Stream<T> implements Transformable<Stream<T>> >
