Methods on structs

All the functions defined for our struct until now are so called associated functions, they are associated with the struct and are called with the syntax:

Struct_name::ass_function() 

We can also define real methods in Rust, that are called on a struct instance and that have a reference to that instance &self as first parameter.

When a specific struct Alien attacks, we can define a method for that Alien struct like this:

fn attack(&self) { 
    println!("I attack! Your health lowers with {} damage points.", self.damage); 
} 

And call it on the function alien berserk as follows:

berserk.attack(); 

A reference to berserk object (the Alien object on which the method is invoked) is passed as &self to the method. In fact the self object is like the self object in Python or this in Java or C#. A method always has &self instance as a parameter, in contrast to a static method.

Here the object is passed immutably, but what if attacking also lowers the Alien structs own...