Rust Essentials - Second Edition

Using the visitor pattern

The visitor design pattern is a common pattern used in object-oriented languages. A visitor stores an algorithm that operates over a collection of objects of different types. It allows multiple different algorithms to be written over the same data without having to modify the code of the data's classes (For a more detailed description, see https://en.wikipedia.org/wiki/Visitor_pattern).

Let's implement a visitor to calculate the area of different geometric objects, such as squares and circles.

// see code in Chapter 6/code/visitor_pattern.rs // structs: struct Point { x: f64, y: f64 } struct Circle { center: Point, radius: f64, } struct Square { lowerLeftCorner: Point, side: f64, } // traits: trait ShapeVisitor { ...