Draft Spec for Second Preview of String Templates (JEP 459)

[Tagir Valeev]

Hello, experts!

Probably it's possible to fix the small thing I wrote before? Namely,
the type of template expression and its thrown exceptions are
determined by the template expression class signature (namely, the
instantiation of R and E generic parameters of Processor) and ignoring
the actual signature of the process() method, which may have covariant
return type and thrown exception type declared. This looks out of sync
with the rest of Java. Example:

public final class TemplateTest {
    interface AnyProcessor extends StringTemplate.Processor<Object,
Throwable> {}

    static class IntProcessor implements AnyProcessor {
       @Override
       public Integer process(StringTemplate stringTemplate) {
          return 123;
       }
    }

    public static void main(String[] args) {
       // error: incompatible types: java.lang.Object cannot be
converted to java.lang.Integer
       Integer xyz = new IntProcessor()."hello";
       // error: unreported exception java.lang.Throwable; must be
caught or declared to be thrown
       Object xyz2 = new IntProcessor()."hello";
    }
}

I'm not sure whether current behavior is explicitly stated in the spec
draft, but the reference implementation behaves this way. I would
expect this code to be compilable.

Note that we have a similar implicit method invocation construct,
try-with-resources, and it respects the actual signature of the
close() method (namely, declared exceptions). I think that similarly
we should respect the actual method signature here.

With best regards,
Tagir Valeev.

On Mon, Oct 9, 2023 at 4:46 PM Gavin Bierman <gavin.bierman at oracle.com> wrote:
>
> Dear experts:
>
> The first draft of a spec covering JEP 459 (String Templates (Second Preview)) is now available at:
>
> https://cr.openjdk.java.net/~gbierman/jep459/latest
>
> Feel free to contact me directly or on this list with any comments.
>
> Thanks
> Gavin
>
>
> > On 5 Oct 2023, at 13:20, Mark Reinhold <mark.reinhold at oracle.com> wrote:
> >
> > https://openjdk.org/jeps/459
> >
> > Summary: Enhance the Java programming language with string
> > templates. String templates complement Java's existing string literals
> > and text blocks by coupling literal text with embedded expressions and
> > template processors to produce specialized results. This is a preview
> > language feature and API.
> >
> > - Mark