Open
Description
Tracking issue for merging: https://github.com/lpxxn/rust-design-pattern/blob/master/structural/decorator.rs
Example:
use std::rc::Rc;
// The base Component trait defines operations that can be altered by
// decorators.
trait Component {
fn operation(&self) -> String;
}
// Concrete Components provide default implementations of the operations.
// There might be several variations of these classes.
struct ConcreteComponent {}
impl Component for ConcreteComponent {
fn operation(&self) -> String {
"ConcreteComponent".to_string()
}
}
// The base Decorator class follows the same interface as the other
// components. The primary purpose of this class is to define the wrapping
// interface for all concrete decorators. The default implementation of the
// wrapping code might include a field for storing a wrapped component and
// the means to initialize it.
trait Decorator: Component {
fn new(component: Rc<dyn Component>) -> Self;
}
// Concrete Decorators call the wrapped object and alter its result in some
// way.
struct ConcreteDecoratorA {
component: Rc<dyn Component>,
}
impl Decorator for ConcreteDecoratorA {
fn new(component: Rc<dyn Component>) -> Self {
ConcreteDecoratorA { component }
}
}
impl Component for ConcreteDecoratorA {
fn operation(&self) -> String {
format!("ConcreteDecoratorA: {}", self.component.operation())
}
}
struct ConcreteDecoratorB {
component: Rc<dyn Component>,
}
impl Decorator for ConcreteDecoratorB {
fn new(component: Rc<dyn Component>) -> Self {
ConcreteDecoratorB { component }
}
}
impl Component for ConcreteDecoratorB {
fn operation(&self) -> String {
format!("ConcreteDecoratorB: {}", self.component.operation())
}
}
// The client code works with all objects using the Component interface.
// This way it can stay independent of the concrete classes of
// components it works with.
struct Client;
impl Client {
fn client_code<T: Component>(component: &T) {
println!("result: {}", component.operation())
}
}
fn main() {
let component = Rc::new(ConcreteComponent {});
println!("client: i get a simple component: ");
Client::client_code(component.as_ref());
println!("client: now I've got a decorated component:");
let decorator_a1 = ConcreteDecoratorA::new(component.clone());
Client::client_code(&decorator_a1);
let decorator_a2 = ConcreteDecoratorB::new(Rc::new(decorator_a1));
Client::client_code(&decorator_a2);
}