Associated functions on structs

Rust makes it possible to call a method in two ways. For example, when we want to obtain the length of a string, you can do:

// see code in Chapter 6/code/paradigm.rs 
let str1 = "abc"; 
println!("{}", str::len(str1)); // 3 
println!("{}", str1.len());     // 3 

The first way is procedural and calls the len function from the str crate in the standard library and passes the string slice str1 as a parameter. The second way which is more object-oriented and more commonly used calls the len method on the string slice str1. If you look it up in the API docs, you can see it has the signature:

   fn len(&self) -> usize 

It effectively takes a reference (&) to self as a parameter.

So we see that Rust caters also for more object-oriented developers, who are used to the object.method() type of notation instead of function(object) type of notation. In Rust, we can define associated functions and methods on a struct, which pretty much compares to the traditional...