Draft JLS Spec about unnamed patterns and variables

[Brian Goetz]

Small wording nit...  in "an unnamed declaration can be used in place of 
the following declarations"

I'm not sure "in place of" is the right wording; I think you may just 
want to say "in", since the grammar permits it in all of these places.  
(What you're really doing here is signalling that there are places the 
grammar allows it, but the semantics do not; you are going to call these 
out individually in the appropriate places.)

Similar for the second "in place of" in this section.

In 14.11.1, I might refactor the text a little further.  The second 
sentence of the first paragraph below is about case constants only, but 
now comes after you talk about case patterns or case constants:

> A|case|label has either one or more|case|constants, ora*one or 
> more*|case|pattern*s*. Every|case|constant must be either (1) 
> the|null|literal, (2) a constant expression (15.29 
> <https://docs.oracle.com/javase/specs/jls/se19/html/jls-15.html#jls-15.29>), 
> or (3) the name of an enum constant (8.9.1 
> <https://docs.oracle.com/javase/specs/jls/se19/html/jls-8.html#jls-8.9.1>); 
> otherwise a compile-time error occurs. A|case|label that has 
> a|null||case|constant may have an optional|default|.
>
> It is a compile-time error if for any|case|label with more than 
> one|case|patterns, any of its|case|patterns declares one or more 
> pattern variables.
>

I suggest:

A|case|label has either one or more|case|constants, ora*one or 
more*|case|pattern*s*.

/For a case label with case constants, /every|case|constant must be 
either (1) the|null|literal, (2) a constant expression (15.29 
<https://docs.oracle.com/javase/specs/jls/se19/html/jls-15.html#jls-15.29>), 
or (3) the name of an enum constant (8.9.1 
<https://docs.oracle.com/javase/specs/jls/se19/html/jls-8.html#jls-8.9.1>); 
otherwise a compile-time error occurs. A|case|label that has 
a|null||case|constant may have an optional|default|.

/For a case label with case patterns/, it is a compile-time error if any 
of its|case|patterns declares one or more pattern variables.

I am not sure about the definition of dominance here.  If I have:

     case Integer _, String _:  A;
     case Number _ : B;

Number dominates Integer, but it doesn't dominate Integer|String.  I 
think you mean "if at least one of pi..pn dominates *all* of the 
patterns ri..rm, no?

But I'm not even sure if this is the right formulation, because:

     sealed interface I permits A, B { }
     record A() implements I {}
     record B() implements I {}

     case A _, B _: ...
     case I i: ...

The first case label dominates I.  So I think you have to appeal to 
exhaustiveness:

"A case label with case patterns p1...pm dominates another case label 
with case patterns q1...qm if the set of patterns { p1..pm } dominates 
each qi", no?

You probably have to slightly refactor the second statement about 
"compile time error if dominance" accordingly.




On 1/26/2023 5:36 AM, Angelos Bimpoudis wrote:
> Dear experts,
>
> The first draft of the JLS spec about unnamed patterns and variables 
> (https://openjdk.org/jeps/8294349) is available at:
>
> https://cr.openjdk.java.net/~abimpoudis/unnamed/latest/
>
> Comments very much welcomed!
> Angelos
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