enhanced enums - back from the dead?

Maurizio Cimadamore maurizio.cimadamore at oracle.com
Wed Dec 5 21:26:08 UTC 2018

Yes, the compiler special cases raw types warnings for j.l.Class type 
arguments and also when doing instanceof. That is, in this program:

import java.util.List;

class Test {
    void test(List<String> ls) {
      ls = (List)null;
      boolean b = (ls instanceof List);
      Class<List> cl = List.class;

There will be no raw warnings - just an unchecked warning in the fist 

The proposed plan for enums is to allow another 'special case' for raw 
enum types.


But a raw warning will be generated for your Iterator example.

On 05/12/2018 19:51, Kevin Bourrillion wrote:
> Liam reminded me,
> 3. the upper bound for class literals, which maybe went without 
> saying, but there it is. Also harmless if I am correct that doing 
> anything with the result of `newInstance` etc. always results in one 
> kind of warning or another.
> Sorry, this is pointless to the real question you're asking, I just 
> hate saying something wrong without correcting it. :-)
> On Wed, Dec 5, 2018 at 11:26 AM Kevin Bourrillion <kevinb at google.com 
> <mailto:kevinb at google.com>> wrote:
>     On Wed, Dec 5, 2018 at 8:19 AM Maurizio Cimadamore
>     <maurizio.cimadamore at oracle.com
>     <mailto:maurizio.cimadamore at oracle.com>> wrote:
>         * Our proposed treatment for generic enums raises an
>         additional, more
>         philosophical, question: what are raw types *for* and how
>         happy are we
>         in seeing more of them (in the form of raw enum types)?
>     I have looked high and low for valid use cases for raw types
>     (apart from interacting with legacy code), and only ever found... two.
>     1. As the stepping stone to make a forbidden cast:
>         @SuppressWarnings("unchecked") // safe because runtime type is
>         functionally covariant
>         Iterator<Object> objects = (Iterator) strings;
>     A common use case for this is to interact with APIs that forgot
>     their wlidcards, but there are plenty of other cases that can't be
>     "fixed".
>     2. As the argument to instanceof. Everyone does it, of course,
>     because writing out `instanceof Map<?, ?>` serves no purpose.
>     Thankfully, they're both harmless... and I believe (?) they were
>     even made exempt from "rawtypes" warnings. (If not, I'd opine that
>     they should be.)
>     -- 
>     Kevin Bourrillion | Java Librarian | Google,
>     Inc. |kevinb at google.com <mailto:kevinb at google.com>
> -- 
> Kevin Bourrillion | Java Librarian | Google, Inc. |kevinb at google.com 
> <mailto:kevinb at google.com>
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