Data classes

Maurizio Cimadamore maurizio.cimadamore at
Thu Nov 2 11:31:06 UTC 2017

Hi Mark,
the code that is generated on a datum is essentially like real code that 
you would otherwise have typed yourself. In other word, think of it as 
ACC_MANDATED, not as ACC_SYNTHETIC. It is something that the compiler 
can fully reason about during type-checking and, as a consequence, it 
means that, yes, you can implement an interface via datum _mandated_ 


On 02/11/17 10:46, Mark Raynsford wrote:
> On 2017-11-01T14:53:40 -0400
> Brian Goetz <brian.goetz at> wrote:
>> At the following URL, please find a writeup containing our current
>> thoughts on Data Classes for Java:
>> Comments welcome!
>> We'll be making a prototype available soon for folks to play with.
> This looks great!
> One thing springs to mind with the accessors: Is it possible that the
> generated accessor methods could participate in the implementation of
> interfaces? For example:
>    interface Vector
>    {
>      double x();
>      double y();
>      double z();
>    }
>    __data class Vector3 (double x, double y, double z)
>      implements Vector { }
> The Vector3 type would automatically get x(), y(), and z() methods
> based on the field declarations. This may imply, of course, that the
> fields are public by default.
> I don't see any obvious reasons why this couldn't work, but you've
> almost certainly thought further than I have on the subject.

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