[External] : Re: [lworld] What is the default of a Primitive.ref variable?

Srikanth Adayapalam srikanth.adayapalam at oracle.com
Fri Jul 23 14:27:08 UTC 2021


Hi Jesper,

The syntax of parameterized primitive types came up earlier for discussion and for good or bad, RefDefault.ref<String>  is the currently blessed syntax and not RefDefault<String>.ref

So, this is a conscious choice that stands for the moment.

There was a push earlier in the day that issues a slightly better diagnostic that what you quote:

"improperly formed type, some parameters are missing or misplaced"

Srikanth

________________________________
From: Jesper Steen Møller <jesper at selskabet.org>
Sent: 23 July 2021 18:37
To: Srikanth Adayapalam <srikanth.adayapalam at oracle.com>
Cc: valhalla-dev <valhalla-dev at openjdk.java.net>
Subject: [External] : Re: [lworld] What is the default of a Primitive.ref variable?


Thanks, Srikanth - but...

... I *did* ask the compiler, but in the context of parameterized types...

public primitive class RefDefault<T> {
    public int i = 1;

    public static void main(String [] args) {
     RefDefault<String>.ref l = RefDefault.ref.default;
     System.out.println(l.i);
    }
}

This gave me a syntax error at the dot in for "RefDefault<String>.ref".

 error: improperly formed type, some parameters are missing
     RefDefault<String>.ref l = RefDefault.ref.default;
                       ^

The compiler will accept RefDefault.ref<String> but that looks off to me. It that the correct form of a reference projection of RefDefault<String>? Or should I fix that in the parser?

It turns out that eliding the type from RefDefault.ref.default (as in RefDefault.ref<String> l = RefDefault.ref.default)ill give a reference to a default value. I'll fix that in bug 8210906.

-Jesper

On 23 Jul 2021, at 13.47, Srikanth Adayapalam <srikanth.adayapalam at oracle.com<mailto:srikanth.adayapalam at oracle.com>> wrote:

You could have asked the compiler ? ��

Prim.ref.default would have the same value and type that an uninitialized field of type Prim.ref would have by default.
Alternately if you do new Prim.ref[10]  the cells of the newly constructed array would have same value and type as
that of Prim.ref.default - so null.

As a result, the program you cite, should fail with NPE and it does on branch tip.

Srikanth
From: valhalla-dev <valhalla-dev-retn at openjdk.java.net<mailto:valhalla-dev-retn at openjdk.java.net>> on behalf of Jesper Steen Møller <jesper at selskabet.org<mailto:jesper at selskabet.org>>
Sent: 23 July 2021 16:17
To: valhalla-dev <valhalla-dev at openjdk.java.net<mailto:valhalla-dev at openjdk.java.net>>
Subject: [lworld] What is the default of a Primitive.ref variable?

Hi list

While making a test case for bug 8210906 (making SomeClass.default a poly-expression if SomeClass is parameterized), I came across the use of .default on a reference, as in

primitive class Prim {
    int i = 42;

    public static void main(String [] args) {
        Prim.ref p = Prim.ref.default; // Does this make sense at all?
        System.out.println(p.i); // Should this NPE or print 0?
    }
}

Prim.ref is the reference projection of Prim, and is nullable, and is reference type. The default of a reference is null.
But what is Prim.ref.default? Is it even a thing? Should it be disallowed?

-Jesper



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