Say that I have the following trait:

trait SayHello {
    fn say_hello(self) -> String;
}

Why can I then do this:

fn say_hello_twice(this: impl SayHello) -> String {
    let said_hello = this.say_hello();
    said_hello + " " + &said_hello
}

But not this:

impl impl SayHello {
    fn say_hello_twice(self) -> String {
        let said_hello = self.say_hello();
        said_hello + " " + &said_hello
    }
}

When the latter is seemingly just syntactic sugar for the former?