Update on String Templates (JEP 459)

[Robbe Pincket]

Hi experts

I thought I’d give my 2 cents here for a sec.

I just looked through this long email chain. I was busy with other things in life so I haven’t checked it out earlier.

First of all, I was surprised it took so long for someone to only apply implicit conversion between `String` and `StringTemplate` only for constant `String`s given that there is already a similar case in the compiler. `int`s can’t be implicitly cast to a `byte`, except (some) constant `int` expressions **can** be implicitly converted to `byte`.

This is by far my favorite suggestion posted so far (and if weren’t suggested yet, I would have). So I’m a bit surprised it seems to have disappeared again.

On another idea going around, using a `$` prefix for string templates and having implicit `String.of(…)` on the “template” if it isn’t there is at the bottom of my list.
The fact that forgetting the `$` prefix just opens you up to an SQL injection attack, while the feature is being advertised as “safe” is for me unacceptable.

(I’m not a big fan of `TEMPLATE"Foo: \{bar}"` either as it’s just so much longer than `"Foo: " + bar`)

I haven’t seen anyone suggesting the opposite though? Have a `$` prefix for standard String interpolation (for those apis that don’t accept a String) and when it’s not there it’s a normal `StringTemplate`. Adding an extra char by accident feels much less likely to me than forgetting one. But I wouldn’t be against having it be something like `STR"..."` instead of `$"..."`.

Combining these would give the following:

```
String s1 = "test" // still a string literal
StringTemplate st2 = "test" // allowed, constant strings can be implicitly converted to templates
StringTemplate st3 = "Foo: \{bar}" // Simple string template

// either
String s4a = $"Foo: \{bar}" // short for String.of("Foo: \{bar}")
String s4b = STR"Foo: \{bar}" // short for String.of("Foo: \{bar}")
```

Kind regards
Robbe Pincket
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