Submitting a JEP

[Daniel Trebbien]

On Fri, Oct 6, 2017 at 7:24 AM, David Lloyd <david.lloyd at redhat.com> wrote:

> On Thu, Oct 5, 2017 at 10:17 PM, Brian Goetz <brian.goetz at oracle.com>
> wrote:
> > The proposal is a bad fit for the assertion facility, since the assertion
> > facility is designed to be disabled, and what you want is something that
> > can't be disabled.
>
> I believe that in the document, Mr. Trebbien explicitly explained why
> the assertion facility is a bad fit, and was specifically not
> suggesting it be used, but rather using it as an example and template
> for the new feature.
>

Specifically, in the Alternatives section (
https://github.com/dtrebbien/JEP-Unreachable-Assertions/blob/master/jep.md#alternatives
), I discuss why neither allowing the proposed "unreachable assertions" to
be disabled, nor amending §14.21 Unreachable Statements to allow
unreachable `assert false' statements, is preferred.

The JLS specifies in §14.10 that an assertion is either enabled or
disabled.  However, the JLS does not specify how assertions are enabled or
disabled.

Unless I am mistaken, there is no standard way to guarantee that assertions
compiled into a CLASS file will be disabled at runtime.  Therefore, unless
the distributor of Java software uses some sort of post-compilation
assertion stripping from CLASS files, the programmers must assume that
assertions might be enabled at runtime.

> But here's an alternative:
> >
> >     throw new UnreachableAssertionException("why");
> >
> > This doesn't need a language feature.
>
> It does, because you cannot put "throw" statements in places where the
> compiler has statically determined that control flow cannot reach,
> which is a key part of the justification of the feature described in
> the document.
>
> This is a feature that I for one have sorely missed for many years
> now, especially in more complex state-oriented code where exit points
> cannot be made visually clear.
>

Yes.  §14.21 Unreachable Statements requires unreachable statements to be
compile-time errors, so you currently cannot place a statement like `throw
new UnreachableAssertionException("why");' at points defined to be
unreachable.