Effective Rust uses a type system to express general behavior

Method

In the Rust type system, behavior first appears when methods are added to data structures: by self-identifying functions that act on instances of that type. This method encapsulates related data and code in a way similar to other Object Oriented languages; however, in Rust, given the widespread use of Rust enumeration types (see item 1), methods can be added to enumeration types in addition to struct types.

enum Shape {
    Rectangle { width: f64, height: f64 },
    Circle { radius: f64 },
}impl Shape {
    pub fn area(&self) -> f64 {
        match self {
            Shape::Rectangle { width, height } => width * height,
            Shape::Circle { radius } => std::f64::consts::PI * radius * radius,
        }
    }
}

The name of a method provides a label for the behavior it encodes, while the method signature provides type information for the input and output. The first input of a method is usually some form of self, indicating the operations the method may perform on the data structure:

• The & selfparameter indicates that the method can read content from the data structure, but does not modify the content.
• The & mut selfparameter indicates that the method may modify the contents of the data structure.
• The selfparameter representation method consumes data structures.

Abstrat behavior