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

[Gavin Bierman]

Hi Tagir,

Apologies for not replying sooner. Yes, this is an excellent suggestion - improving the precision of typing template expressions is a very welcome change :-)

I have updated the spec, and the compiler will be updated shortly.

Thanks,
Gavin

> On 10 Oct 2023, at 06:33, Tagir Valeev <amaembo at gmail.com> wrote:
> 
> 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