lazy evaluation of string templates

[@gavinking] The spec promises that string templates are lazily evaluated, but dodges the question of how exactly that works. This is actually a bit of a tricky problem if we want to continue to support the syntax:

String s = "Hello, " name "!";

Let me run through several options:

• Don’t support the above syntax. A string template is a StringTemplate. If you want to get a String out of it, you have to call string explicitly.
• A string template is just a String. To re-evaluate it, you call interpolate() to get a new String. This doesn’t work out if we continue to lower String to java.lang.String, but if we decide to change our minds about that (it is on the cards), then it could work.
• Make string interpolation eager all the time. To get lazy evaluation you write () "Hello, " name "!", or use some other weird syntax to get a String() instead of a String.

Thoughts?

[Migrated from ceylon/ceylon-spec#345]

[gavinking]

These days, we can just write (name) => "Hello, " name "!" and that’s fine. Closing this very ancient and obsolete issue.

[gavinking]

@xkr47 yeah, sure, I copy/pasted from the very ancient issue description.