Update on String Templates (JEP 459)

[Remi Forax]

----- Original Message -----
> From: "Guy Steele" <guy.steele at oracle.com>
> To: "John Rose" <john.r.rose at oracle.com>
> Cc: "Tagir Valeev" <amaembo at gmail.com>, "Brian Goetz" <brian.goetz at oracle.com>, "amber-spec-experts"
> <amber-spec-experts at openjdk.org>
> Sent: Wednesday, March 13, 2024 9:13:30 PM
> Subject: Re: Update on String Templates (JEP 459)

>> On Mar 13, 2024, at 3:33 PM, John Rose <john.r.rose at oracle.com> wrote:
>> 
>> On 9 Mar 2024, at 3:48, Tagir Valeev wrote:
>> 
>>> The idea is interesting. There's a thing that disturbs me though.
>>> Currently, proc."string" and proc."string \{template}" are uniformly
>>> processed, and the processor may not care much about whether it's a string
>>> or a template: both can be processed uniformly. After this change, removing
>>> the last embedded expression from the template (e.g., after inlining a
>>> constant) will implicitly change the type of the literal from
>>> StringTemplate to String. This may either cause a compilation error, or
>>> silently bind to another overload which may or may not behave like a
>>> template overload with a single-fragment-template. For API authors, this
>>> means that every method accepting StringTemplate should have a counterpart
>>> accepting String. The logic inside both methods would likely be very
>>> similar, so probably both will eventually call a third private method. For
>>> API user, it could be unclear how to call a method accepting StringTemplate
>>> if I have simple string in hands but there's no String method (or it does
>>> slightly different thing due to poor API design). Should I use some ugly
>>> construct like "This is a string but the API wants a template, so I append
>>> an empty embedded expression\{""}"?
>> 
>> This is a huge thread that I hesitate to dive into, but here’s me putting in one
>> toe:  Why do we care so much about no-arg string templates?  It’s a small
>> corner case!  The workarounds (for the no-arg case) are totally straightforward
>> even if the string template literals (as a syntax) are required to have at
>> least one argument.
>> 
>> Can we have a plausible use case, please, for why a ST with no arguments would
>> be important, so important that we are motived to invent a sigil syntax or
>> special type system rules, to avoid requiring the user to invoke a static
>> factory?
>> 
>> Also, Tagir’s workaround of adding a fake argument looks like it would work just
>> fine, of course depending on which processor was eventually used.
>> 
>> And in that vein let me add one new (very bike-sheddy) suggestion before I beat
>> a hasty retreat:  Instead of in (1) a sigil before the quote like Guy’s
>> $"hello", put it (1b) after the quote, and in the ST case only.  The ST syntax
>> could explicitly allow that a no-arg string template would be spelled with a
>> leading sequence "\{}... which looks like the coder started writing a ST
>> argument, but in fact dropped it.  So "hello" is a 5-char string, in any
>> context.  And "\{}hello" is a 5-char no-arg string template, in any context.
>> That’s Tagir’s workaround, elevated a bit into a new corner case of (existing)
>> syntax.
>> 
>> But even that teeny bit of syntax strikes me as overkill, because I don’t see
>> the importance of the use cases (no-arg STs) it helps.  Just call
>> ST.of("hello") and call it a day.
>> 
>> In any case, it seems fine to let the IDE take the lead with no-arg STs, helping
>> the user decide when and how to disambiguate strings from no-arg STs.  Putting
>> in syntax or type system help for this is surely more expensive than punting to
>> the IDE, unless there is going to be heavy use of no-arg STs for some use cases
>> I am not seeing.
> 
> Well, just off the top of my head as a thought experiment, if I had a series of
> SQL commands to process, some with arguments and some not, I would rather write
> 
> SQL.process($”CREATE TABLE foo;”);
> SQL.process($”ALTER TABLE foo ADD name varchar(40);”);
> SQL.process($”ALTER TABLE foo ADD title varchar(30);”);
> SQL.process($”INSERT INTO foo (name, title) VALUES (‘Guy’, ‘Hacker’);”);
> SQL.process($”INSERT INTO foo (name, title) VALUES (\{other name}, \{other
> job});”);
> 
> than
> 
> SQL.process(ST.of(”CREATE TABLE foo;”));
> SQL.process(ST.of(”ALTER TABLE foo ADD name varchar(40);”));
> SQL.process(ST.of(”ALTER TABLE foo ADD title varchar(30);”));
> SQL.process(ST.of(”INSERT INTO foo (name, title) VALUES (‘Guy’, ‘Hacker’);”));
> SQL.process(”INSERT INTO foo (name, title) VALUES (\{other name}, \{other
> job});”);
> 
> especially if I thought that maybe down the road I might want to change the
> constants 30 and 40 and ‘Hacker' to variables. I don't want to have to keep
> adding and deleting calls to ST.of as I edit the template strings during
> program development to have different numbers of interpolated expressions.

Given what Maurizio said and this, i think the only missing piece in the puzzle is what about existing methods taking a String as parameter.

We know that for SQL.process(), we do not want process() to take a String but only a StringTemplate.
But what about the existing methods that takes a String.

Given a method Logger.warning(String), should
  LOG.warning($”CREATE TABLE foo;”);
  LOG.warning($”INSERT INTO foo (name, title) VALUES (\{other name}, \{other job});”);

be legal ? Is there an auto-conversion (a kind of boxing conversion) from StringTemplate to String ?


> 
> —Guy

Rémi