Flexible constructors: dubious error

[Archie Cobbs]

Hi Stephan,

On Tue, Oct 29, 2024 at 9:11 AM Stephan Herrmann <stephan.herrmann at berlin.de>
wrote:

> Am 29.10.24 um 14:11 schrieb Olexandr Rotan:
> > Local classes, as well as inner ones (don't confuse with nested)
> implicitly take
> > parents "this" as a constructor argument
>
> They *may* take this argument *if needed*.
>
> But this is more an implementation detail and not the level at which the
> specification defines this, is it?
>

This is a specification thing.

Here is what is "supposed" to happen: Both "Local" classes in the example
are declared prior to super(). These classes are therefore within an early
construction context of "Inner" and therefore do not have access to the
current instance of "Inner" - but this access would be required for the
expression "s" which is short-hand for "Inner.this.s".

So the reference to "s" should generate an error, which happens with the
current 24 build:

    X.java:14: error: cannot reference s before supertype constructor has
been called
                                                System.out.println(s);
                                                                   ^

FYI there is still an outstanding bug and associated PR
<https://github.com/openjdk/jdk/pull/21410> related to this situation, so
with the current 24 build you also get these (bogus) errors:

    X.java:7: error: cannot reference this before supertype constructor has
been called
                                new Local() {};
                                            ^
    X.java:12: error: cannot reference this before supertype constructor
has been called
                                new Local() {
                                            ^

Those errors are bogus, because under the latest "flexible constructors"
spec, local classes declared in an early construction context of class C
are treated the same as anonymous classes in that situation - they do not
have any outer instance of type C - so you can declare and instantiate them
freely.

-Archie

-- 
Archie L. Cobbs
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