JDK-8300786 - No longer require super() and this() to appear first in a constructor

Archie Cobbs archie.cobbs at gmail.com
Thu Feb 2 20:09:25 UTC 2023

On Tue, Jan 31, 2023 at 2:45 PM Archie Cobbs <archie.cobbs at gmail.com> wrote:

> Obviously this change requires a JEP, and so we have this JEP draft for
> review:
> JDK-8300786 <https://bugs.openjdk.org/browse/JDK-8300786> - No longer
> require super() and this() to appear first in a constructor

Update on this JEP.

Doing a little more research I discovered that since Java 8 the compiler
has not been following the spec as it applies to allowing type parameters
inside super() calls (bug filed as JDK-8301649

The spec says this is a "static context", so type parameters are in theory
not allowed. But the compiler allows it, and in fact it seems the spec is
being too restrictive.

With the change in this JEP, this discrepancy will only get worse, because
the "static context" that's part of a constructor can now include a lot
more stuff.

In this discussion on compiler-dev
it was generally agreed that the spec should probably be fixed as part of
this JEP.

So I'm wondering about people's thoughts on this list - not only whether to
fix the spec, but also how exactly to do so, any other suggestions, etc.

I see two options:

   1. Split "static context" in two:
   1. The old "static context" gets renamed to "lexically static context".
      References to anything non-static are disallowed - same as now.
      2. Define a new "referentially static context" which disallows any
      references to 'this' (explicit or implicit) but allows type
parameters, etc.
   2. Leave "static context" alone, but add an exception to how it applies
   prior to super() so that it permits type parameters, etc.

Or maybe there is another option... ?



Archie L. Cobbs
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