Стратегія — це поведінковий патерн, який виносить набір алгоритмів у власні класи і робить їх взаємозамінними.
Інші об’єкти містять посилання на об’єкт-стратегію та делегують їй роботу. Програма може підмінити цей об’єкт іншим, якщо потрібен інший спосіб вирішення завдання.
/// 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
