Strategy em Rust

O Strategy é um padrão de projeto comportamental que transforma um conjunto de comportamentos em objetos e os torna intercambiáveis dentro do objeto de contexto original.

O objeto original, chamado contexto, mantém uma referência a um objeto strategy e o delega a execução do comportamento. Para alterar a maneira como o contexto executa seu trabalho, outros objetos podem substituir o objeto strategy atualmente vinculado por outro.

Saiba mais sobre o Strategy

Conceptual Example

A conceptual Strategy example via traits.

conceptual.rs

/// Defines an injectable strategy for building routes.
trait RouteStrategy {
    fn build_route(&self, from: &str, to: &str);
}

struct WalkingStrategy;

impl RouteStrategy for WalkingStrategy {
    fn build_route(&self, from: &str, to: &str) {
        println!("Walking route from {} to {}: 4 km, 30 min", from, to);
    }
}

struct PublicTransportStrategy;

impl RouteStrategy for PublicTransportStrategy {
    fn build_route(&self, from: &str, to: &str) {
        println!(
            "Public transport route from {} to {}: 3 km, 5 min",
            from, to
        );
    }
}

struct Navigator<T: RouteStrategy> {
    route_strategy: T,
}

impl<T: RouteStrategy> Navigator<T> {
    pub fn new(route_strategy: T) -> Self {
        Self { route_strategy }
    }

    pub fn route(&self, from: &str, to: &str) {
        self.route_strategy.build_route(from, to);
    }
}

fn main() {
    let navigator = Navigator::new(WalkingStrategy);
    navigator.route("Home", "Club");
    navigator.route("Club", "Work");

    let navigator = Navigator::new(PublicTransportStrategy);
    navigator.route("Home", "Club");
    navigator.route("Club", "Work");
}

Output

Walking route from Home to Club: 4 km, 30 min
Walking route from Club to Work: 4 km, 30 min
Public transport route from Home to Club: 3 km, 5 min
Public transport route from Club to Work: 3 km, 5 min

Functional approach

Functions and closures simplify Strategy implementation as you can inject behavior right into the object without complex interface definition.

It seems that Strategy is often implicitly and widely used in the modern development with Rust, e.g. it’s just like iterators work:

let a = [0i32, 1, 2];

let mut iter = a.iter().filter(|x| x.is_positive());

functional.rs

type RouteStrategy = fn(from: &str, to: &str);

fn walking_strategy(from: &str, to: &str) {
    println!("Walking route from {} to {}: 4 km, 30 min", from, to);
}

fn public_transport_strategy(from: &str, to: &str) {
    println!(
        "Public transport route from {} to {}: 3 km, 5 min",
        from, to
    );
}

struct Navigator {
    route_strategy: RouteStrategy,
}

impl Navigator {
    pub fn new(route_strategy: RouteStrategy) -> Self {
        Self { route_strategy }
    }

    pub fn route(&self, from: &str, to: &str) {
        (self.route_strategy)(from, to);
    }
}

fn main() {
    let navigator = Navigator::new(walking_strategy);
    navigator.route("Home", "Club");
    navigator.route("Club", "Work");

    let navigator = Navigator::new(public_transport_strategy);
    navigator.route("Home", "Club");
    navigator.route("Club", "Work");

    let navigator = Navigator::new(|from, to| println!("Specific route from {} to {}", from, to));
    navigator.route("Home", "Club");
    navigator.route("Club", "Work");
}

Output

Walking route from Home to Club: 4 km, 30 min
Walking route from Club to Work: 4 km, 30 min
Public transport route from Home to Club: 3 km, 5 min
Public transport route from Club to Work: 3 km, 5 min
Specific route from Home to Club
Specific route from Club to Work

Strategy em Rust

Conceptual Example

conceptual.rs

Output

Functional approach

functional.rs

Output

Strategy em outras linguagens