Proposal: Simplified syntax for dealing with parameterized types. (original) (raw)

Joseph D. Darcy Joe.Darcy at Sun.COM
Mon Mar 23 18:16:48 PDT 2009

james lowden wrote:

Yeah, the "Map<String, String> map = new HashMap<>();" is a lot simpler (and something I've wanted. . .); I'd actually like to see both that and the ideas I've suggested implemented. . .

Yes, Jeremy sent around a proposal for that in the first days of the call for proposals; a revised is in the works.

I may be attempting to kill multiple birds with one stone here; part of it is removing repitition from code, which the previously-floated proposal addresses. The other thing I'm trying to do is provide an "easier" way to use parameterized types in a type-safe fashion, without (unfortunately, in my mind) providing some kind of reification.

I'm thinking of two different kinds of "type safety". One is making it harder to "break" the parameterized type (by, for example, setting a HashMap<String,String> reference to a plain HashMap); the subclassing provides this.

The concerns you have with converting to/from rawtypes could be handled with either new lint flags to the compiler or annotation processors to reject such conversions.

The other feature I'm looking for is some kind of differentiation-of-intent;

Declaring a new type strikes me as a fine way to indicate differentiation of intent :-)

Therefore, combined with the shorter declaration syntax and the ability to cause compilation errors for raw types without change the language, I don't see a strong motivation for this change.

Java already has this in the case of enums (i.e., any given four-value enum is in some sense "equivalent" to any other, as they are both internally represented by one of four integer values, but you can't interconvert);

In their serial form, enums are represented by their names, not their ordinal values. Also, enums can and do define type-specific behavior.
Therefore, all enums with the same number of constants are not semantically equivalent.

-Joe

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