Draft JEP on Primitive types in patterns, instanceof, and switch

[Brian Goetz]

Yes, pardon my quick typing.

More specifically, a case constant is not a _constant pattern_ (at 
least, not yet), it is just a constant case label. Constants are typed, 
and they carray both a type match and a value match.  When you say

     case 0

this is a constant for an int, and doesn't match a floating point zero 
(if the match target is `float`, it won't even compile.)  Similarly, 
`case 0.0` is a constant for a float, and is not applicable to a match 
target of int.  (We do have the usual tolerance for matching int 
constants to shorter int types, as before.)

We may generalize these to constant patterns in the future, but right 
now, these are constant case labels and their semantics are derived from 
that of existing case labels.

On 1/26/2023 10:25 AM, Guy Steele wrote:
>
>
>> On Jan 26, 2023, at 9:36 AM, Brian Goetz <brian.goetz at oracle.com> wrote:
>>
>> ...
>>
>> For comparing a variable to a constant, representational equality is 
>> the obvious interpretation; `case nnn` means "is it the number nnn".  
>> This allows you to say `case NaN` and `case -0` and get the right 
>> answer (all of these relations agree on what to do about 1.0).
>
> Careful: I think you had better say “case -0.0”; otherwise the 
> constant expression “-0” will be reduced to “0” and only then 
> converted to floating-point representation, producing +0.0.
>
> Yes, floating-point is VERY fiddly.
>
> —Guy
>
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