Kotlin statics and static extensions

[elizarov]

This is the initial proposal for Kotlin statics and static extensions

[valery1707]

Missing character ` in heading of last table:

• Actual:

  | Alternative  | Scheme                  | `Color.background` on JVM | Color.parse` on JVM | `Box.of` on JVM |
  

• Fixed:

  | Alternative  | Scheme                  | `Color.background` on JVM | `Color.parse` on JVM | `Box.of` on JVM |
  

[ilya-g]

Suggested change

	> This means, that removing a `static` modifier to an object declaration is not a source-compatible change,
	> This means, that removing a `static` modifier from an object declaration is not a source-compatible change,

[ilya-g]

Are "static extensions as static members" disallowed or just the corresponding section is omitted?
E.g static fun Int.static.ext()

[ilya-g]

File classes do not have any constructor, and it is not possible to instantiate them from Java despite the IDE thinking otherwise.
Despite that (file classes not having a constructor at all) it looks like an omission rather than a deliberate decision, so IMO it would be better not to replicate it in static objects, and generate an explicit private constructor.

[elizarov]

They do have a constructor and can be, in fact, instantiated from Java (albeit IDEA gives a warning "Instantiation of utility class"). Every JVM class has a "default" constructor, unless a constructor is explicitly specified.

[ilya-g]

They don't. I've checked.

[dkhalanskyjb]

There is. This code compiles without issues:

trait Read {
    fn read() -> Self;
}

struct X;

impl Read for X {
    fn read() -> X {
        X
    }
}

struct Y;

impl Read for Y {
    fn read() -> Y {
        Y
    }
}


fn main() {
    let x: X = Read::read();
}