location / scoping of Impl

[stroucki]

Hi,

I am learning Rust via rust-book.cs.brown.edu and I think one of the examples had an Impl for a struct placed within a function. So I was thinking about where Impls can be placed, and whether they can be out of scope. I wrote up the below code (without the added scoping) and it worked. However, it still worked when I added a layer of scoping as below.

I consulted a friend who said this may warrant a warning from the compiler, and I should create an issue for it.

struct Foo {
  x: i32,
}

pub fn main() {
{ // will still work with or without this extra scope
  impl Foo {
    fn inc(&mut self) {
      self.x+=1;
    }
  }
} // extra scope

  let mut test = Foo{ x:1 };
  test.inc();
  println!("Foo: {}", test.x);
}

Rustc version: rustc 1.75.0 (82e1608 2023-12-21) (built from a source tarball)

[Urgau]

See RFC 3373: Avoid non-local definitions in functions.

It's currently being implemented in #120393.