compareTo and deriving

Zheka Kozlov orionllmain at
Mon Dec 4 14:19:10 UTC 2017

What is the implementation of compareTo() for Point?

2017-12-04 20:34 GMT+07:00 Remi Forax <forax at>:

> Ok,
> record/data class currently provides getters and toString/equals/hashCode,
> what if i want to add a compareTo.
> In Haskell, it's easy, one can use 'deriving', in Java, it can be written
> that way,
>   record Point(int x, int y) implements Comparable<Point>
>     deriving equals, hashCode, toString, compareTo;
> For the compiler, the method exists in the supertypes, so the signature of
> the method can be computed from the super types,
> after each generated method use an invokedynamic with the same meta
> protocol (a list of getters),
> so if by convention "equals", "hashCode", "toString", "compareTo" are the
> names of some bootstrap methods in a class DerivingMetaFactory,
> it can be trivial for a JDK developer to add a new bootstrap method
> without having to change the JLS.
> So my point is, that we can specify once how the compiler should generate
> codes for any generated methods in an extensible way.
> regards,
> Rémi

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