self when used as first method argument, is a shorthand for self: Self. There are also &self, which is equivalent to self: &Self, and &mut self, which is equivalent to self: &mut self.
Self in method arguments is syntactic sugar for the receiving type of the method (i.e. the type whose impl this method is in). This also allows for generic types without too much repetition.
https://stackoverflow.com/questions/32304595/whats-the-difference-between-self-and-self
