this is commonly used with a similar meaning to self in cases where self can’t be used because it is a reserved keyword.

Example:

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> {
        let this = self.project();
        this.inner.poll_next(cx)
    }

https://github.com/rust-lang/futures-rs/blob/master/futures-util/src/stream/select.rs#L113-L116

I do run into them even though I use Rust for ~3 years now, but only in non-obvious cases, e. g. when all references to the borrowed data are dropped before the end of the function.

Rust would be some borrow checker compile error like

borrowed data escapes outside of associated function

argument requires that `'1` must outlive `'static`

Free standing functions in Java?! This can’t be true.

Still better than having to create a new class just to implement

public static void main(String[] args) {}

Relevant Fireship video: https://youtu.be/m4-HM_sCvtQ