On 28 Sep 2022, at 13:49, Remi Forax wrote:
- We should not be able to declare fields inside a classless class,
students strugle at the beginning to make the difference between a
field and a local variable.
Every syntax that make that distinction murkier is a bad idea.
So perhaps what we want is a classless container of methods, not a
classless class.
Hmmm… That would be an interface. I’ll pull on that thread a
little:
An interface has no non-static fields and (bonus) its static fields are
always constant. So you can teach interface *as a container* without
getting into mutability.
Methods would have to be implicitly decorated with `default` in an
anonymous *interface*.
The execution of an instance-main anonymous interface would look almost
*exactly* like that for a class:
`public static void main(String[] av) { new <ThisClass>(){}.main(); }`
The only difference is the `{}`. Abstracts would be forbidden in an
anonymous interface: Every method has a body, just as every field has
an initializer.
Bonus: No instance initializers, since it’s an interface. (No
constructors either.) So the headaches about initialization-related
syntaxes go away without additional special pleading.
Objection: *That’s no interface!* Well, true. Except it is an
interface to the system, being a launch point. (Is that just a bad
pun?) Also, folks use interfaces today as an idiom for a lightweight
container of Java code (at least, I do that).
Bonus: If the “instance main” feature is supported *only for
interface containers* then some issues of accidentally creating a main
(in existing code) go away, simply because the attack surface (for
accidents) gets smaller. Yes, that’s a yucky bonus.
