Update on String Templates (JEP 459)

[Guy Steele]

Second thoughts about how to explain a string interpolation literal:

> On Mar 13, 2024, at 2:02 PM, Guy Steele <guy.steele at oracle.com> wrote:
> . . .
> 
> —————————
> String is not a subtype of StringTemplate; they are disjoint types.
> 
> 	$”foo”              is a (trivial) string template literal
> 	“foo”                is a string literal
>         $”Hello, \{x}”     is a (nontrivial) string template literal
>         “Hello, \{x}”      is a shorthand (expanded by the compiler) for `String.of($“Hello, \{x}”)`
> —————————

Given that the intent is that String.of (or whatever we want to call it—possibly the `interpolation` instance method of class `StringTemplate` rather than a static method `String.of`) should just do standard string concatenation, we might be better off just saying that a string interpolation literal is expanded by the compiler into uses of “+”; for example,

         “Hello, \{x}.”

(I have added a period to the example to make the point clearer) is expanded into

        “Hello, “ + x + “.”

and in general

        “c0\{e1}c1\{e2}c2…\{en}cn”

(where each ck is a possibly empty sequence of string characters and each ek is an expression)  is expanded into

        “c0” + (e1) + “c1” + (e2) + “c2” + … + (en) + “cn”

The point is that, with this definition, “c0\{e1}c1\{e2}c2…\{en}cn” is a constant expression iff every ek is a constant expression. This is handy for interpolating constant variables into a string that is itself intended to be constant.

—Guy