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Flyweight

Flyweight en TypeScript

Flyweight es un patrón de diseño estructural que permite a los programas soportar grandes cantidades de objetos manteniendo un bajo uso de memoria.

El patrón lo logra compartiendo partes del estado del objeto entre varios objetos. En otras palabras, el Flyweight ahorra memoria RAM guardando en caché la misma información utilizada por distintos objetos.

Complejidad:

Popularidad:

Ejemplos de uso: El patrón Flyweight tiene un único propósito: minimizar el consumo de memoria. Si tu programa no tiene problemas de escasez de RAM, puedes ignorar este patrón por una temporada.

Identificación: El patrón Flyweight puede reconocerse por un método de creación que devuelve objetos guardados en caché en lugar de crear objetos nuevos.

Ejemplo conceptual

Este ejemplo ilustra la estructura del patrón de diseño Flyweight y se centra en las siguientes preguntas:

  • ¿De qué clases se compone?
  • ¿Qué papeles juegan esas clases?
  • ¿De qué forma se relacionan los elementos del patrón?

index.ts: Ejemplo conceptual

/**
 * The Flyweight stores a common portion of the state (also called intrinsic
 * state) that belongs to multiple real business entities. The Flyweight accepts
 * the rest of the state (extrinsic state, unique for each entity) via its
 * method parameters.
 */
class Flyweight {
    private sharedState: any;

    constructor(sharedState: any) {
        this.sharedState = sharedState;
    }

    public operation(uniqueState): void {
        const s = JSON.stringify(this.sharedState);
        const u = JSON.stringify(uniqueState);
        console.log(`Flyweight: Displaying shared (${s}) and unique (${u}) state.`);
    }
}

/**
 * The Flyweight Factory creates and manages the Flyweight objects. It ensures
 * that flyweights are shared correctly. When the client requests a flyweight,
 * the factory either returns an existing instance or creates a new one, if it
 * doesn't exist yet.
 */
class FlyweightFactory {
    private flyweights: {[key: string]: Flyweight} = <any>{};

    constructor(initialFlyweights: string[][]) {
        for (const state of initialFlyweights) {
            this.flyweights[this.getKey(state)] = new Flyweight(state);
        }
    }

    /**
     * Returns a Flyweight's string hash for a given state.
     */
    private getKey(state: string[]): string {
        return state.join('_');
    }

    /**
     * Returns an existing Flyweight with a given state or creates a new one.
     */
    public getFlyweight(sharedState: string[]): Flyweight {
        const key = this.getKey(sharedState);

        if (!(key in this.flyweights)) {
            console.log('FlyweightFactory: Can\'t find a flyweight, creating new one.');
            this.flyweights[key] = new Flyweight(sharedState);
        } else {
            console.log('FlyweightFactory: Reusing existing flyweight.');
        }

        return this.flyweights[key];
    }

    public listFlyweights(): void {
        const count = Object.keys(this.flyweights).length;
        console.log(`\nFlyweightFactory: I have ${count} flyweights:`);
        for (const key in this.flyweights) {
            console.log(key);
        }
    }
}

/**
 * The client code usually creates a bunch of pre-populated flyweights in the
 * initialization stage of the application.
 */
const factory = new FlyweightFactory([
    ['Chevrolet', 'Camaro2018', 'pink'],
    ['Mercedes Benz', 'C300', 'black'],
    ['Mercedes Benz', 'C500', 'red'],
    ['BMW', 'M5', 'red'],
    ['BMW', 'X6', 'white'],
    // ...
]);
factory.listFlyweights();

// ...

function addCarToPoliceDatabase(
    ff: FlyweightFactory, plates: string, owner: string,
    brand: string, model: string, color: string,
) {
    console.log('\nClient: Adding a car to database.');
    const flyweight = ff.getFlyweight([brand, model, color]);

    // The client code either stores or calculates extrinsic state and passes it
    // to the flyweight's methods.
    flyweight.operation([plates, owner]);
}

addCarToPoliceDatabase(factory, 'CL234IR', 'James Doe', 'BMW', 'M5', 'red');

addCarToPoliceDatabase(factory, 'CL234IR', 'James Doe', 'BMW', 'X1', 'red');

factory.listFlyweights();

Output.txt: Resultado de la ejecución

FlyweightFactory: I have 5 flyweights:
Chevrolet_Camaro2018_pink
Mercedes Benz_C300_black
Mercedes Benz_C500_red
BMW_M5_red
BMW_X6_white

Client: Adding a car to database.
FlyweightFactory: Reusing existing flyweight.
Flyweight: Displaying shared (["BMW","M5","red"]) and unique (["CL234IR","James Doe"]) state.

Client: Adding a car to database.
FlyweightFactory: Can't find a flyweight, creating new one.
Flyweight: Displaying shared (["BMW","X1","red"]) and unique (["CL234IR","James Doe"]) state.

FlyweightFactory: I have 6 flyweights:
Chevrolet_Camaro2018_pink
Mercedes Benz_C300_black
Mercedes Benz_C500_red
BMW_M5_red
BMW_X6_white
BMW_X1_red

Flyweight en otros lenguajes

Flyweight en C# Flyweight en C++ Flyweight en Go Flyweight en Java Flyweight en PHP Flyweight en Python Flyweight en Ruby Flyweight en Rust Flyweight en Swift