As we've seen before, when we implement behavior for a type, the functions we define have self, &self, or &mut self as the first parameter. We now understand enough to recognize that that means that self is either moved (or copied) into the scope of the function, borrowed, or mutably borrowed. Which one we choose to use can have some pretty important consequences.
The data type of self is implicit: it's got to be the data type we're implementing the function on and, because of that, we don't get to specify the data type for self as part of the parameter list. Since there is no data type to prefix & or &mut to, we are allowed to write them before self instead.
In all three cases, self means the data value that this function was called through. If we have a u32 variable named x and we tell Rust to x.pow(3), the...