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Poids mouche

Poids mouche en C#

Le poids mouche est un patron de conception structurel qui permet à des programmes de limiter leur consommation de mémoire malgré un très grand nombre d’objets.

Ce patron est obtenu en partageant des parties de l’état d’un objet à plusieurs autres objets. En d’autres termes, le poids mouche économise de la RAM en mettant en cache les données identiques chez différents objets.

Utilisation du patron de conception en C#

Complexité :

Popularité :

Exemples d’utilisation : Le poids mouche n’a qu’une seule utilité : minimiser l’utilisation de la mémoire. Si votre programme ne rencontre aucun problème de RAM, ignorez ce patron pour le moment.

Identification : Le poids mouche peut être reconnu par une méthode de création qui renvoie des objets du cache plutôt que d’en créer de nouveaux.

Exemple conceptuel

Dans cet exemple, nous allons voir la structure du Poids mouche. Nous allons répondre aux questions suivantes :

  • Que contiennent les classes ?
  • Quels rôles jouent-elles ?
  • Comment les éléments du patron sont-ils reliés ?

Program.cs: Exemple conceptuel

using System;
using System.Collections.Generic;
using System.Linq;
// Use Json.NET library, you can download it from NuGet Package Manager
using Newtonsoft.Json;

namespace RefactoringGuru.DesignPatterns.Flyweight.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.
    public class Flyweight
    {
        private Car _sharedState;

        public Flyweight(Car car)
        {
            this._sharedState = car;
        }

        public void Operation(Car uniqueState)
        {
            string s = JsonConvert.SerializeObject(this._sharedState);
            string u = JsonConvert.SerializeObject(uniqueState);
            Console.WriteLine($"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.
    public class FlyweightFactory
    {
        private List<Tuple<Flyweight, string>> flyweights = new List<Tuple<Flyweight, string>>();

        public FlyweightFactory(params Car[] args)
        {
            foreach (var elem in args)
            {
                flyweights.Add(new Tuple<Flyweight, string>(new Flyweight(elem), this.getKey(elem)));
            }
        }

        // Returns a Flyweight's string hash for a given state.
        public string getKey(Car key)
        {
            List<string> elements = new List<string>();

            elements.Add(key.Model);
            elements.Add(key.Color);
            elements.Add(key.Company);

            if (key.Owner != null && key.Number != null)
            {
                elements.Add(key.Number);
                elements.Add(key.Owner);
            }

            elements.Sort();

            return string.Join("_", elements);
        }

        // Returns an existing Flyweight with a given state or creates a new
        // one.
        public Flyweight GetFlyweight(Car sharedState)
        {
            string key = this.getKey(sharedState);

            if (flyweights.Where(t => t.Item2 == key).Count() == 0)
            {
                Console.WriteLine("FlyweightFactory: Can't find a flyweight, creating new one.");
                this.flyweights.Add(new Tuple<Flyweight, string>(new Flyweight(sharedState), key));
            }
            else
            {
                Console.WriteLine("FlyweightFactory: Reusing existing flyweight.");
            }
            return this.flyweights.Where(t => t.Item2 == key).FirstOrDefault().Item1;
        }

        public void listFlyweights()
        {
            var count = flyweights.Count;
            Console.WriteLine($"\nFlyweightFactory: I have {count} flyweights:");
            foreach (var flyweight in flyweights)
            {
                Console.WriteLine(flyweight.Item2);
            }
        }
    }

    public class Car
    {
        public string Owner { get; set; }

        public string Number { get; set; }

        public string Company { get; set; }

        public string Model { get; set; }

        public string Color { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            // The client code usually creates a bunch of pre-populated
            // flyweights in the initialization stage of the application.
            var factory = new FlyweightFactory(
                new Car { Company = "Chevrolet", Model = "Camaro2018", Color = "pink" },
                new Car { Company = "Mercedes Benz", Model = "C300", Color = "black" },
                new Car { Company = "Mercedes Benz", Model = "C500", Color = "red" },
                new Car { Company = "BMW", Model = "M5", Color = "red" },
                new Car { Company = "BMW", Model = "X6", Color = "white" }
            );
            factory.listFlyweights();

            addCarToPoliceDatabase(factory, new Car {
                Number = "CL234IR",
                Owner = "James Doe",
                Company = "BMW",
                Model = "M5",
                Color = "red"
            });

            addCarToPoliceDatabase(factory, new Car {
                Number = "CL234IR",
                Owner = "James Doe",
                Company = "BMW",
                Model = "X1",
                Color = "red"
            });

            factory.listFlyweights();
        }

        public static void addCarToPoliceDatabase(FlyweightFactory factory, Car car)
        {
            Console.WriteLine("\nClient: Adding a car to database.");

            var flyweight = factory.GetFlyweight(new Car {
                Color = car.Color,
                Model = car.Model,
                Company = car.Company
            });

            // The client code either stores or calculates extrinsic state and
            // passes it to the flyweight's methods.
            flyweight.Operation(car);
        }
    }
}

Output.txt: Résultat de l’exécution

FlyweightFactory: I have 5 flyweights:
Camaro2018_Chevrolet_pink
black_C300_Mercedes Benz
C500_Mercedes Benz_red
BMW_M5_red
BMW_white_X6

Client: Adding a car to database.
FlyweightFactory: Reusing existing flyweight.
Flyweight: Displaying shared {"Owner":null,"Number":null,"Company":"BMW","Model":"M5","Color":"red"} and unique {"Owner":"James Doe","Number":"CL234IR","Company":"BMW","Model":"M5","Color":"red"} state.

Client: Adding a car to database.
FlyweightFactory: Can't find a flyweight, creating new one.
Flyweight: Displaying shared {"Owner":null,"Number":null,"Company":"BMW","Model":"X1","Color":"red"} and unique {"Owner":"James Doe","Number":"CL234IR","Company":"BMW","Model":"X1","Color":"red"} state.

FlyweightFactory: I have 6 flyweights:
Camaro2018_Chevrolet_pink
black_C300_Mercedes Benz
C500_Mercedes Benz_red
BMW_M5_red
BMW_white_X6
BMW_red_X1

Poids mouche dans les autres langues

Patrons de conception : Poids mouche en Java Patrons de conception : Poids mouche en C++ Patrons de conception : Poids mouche en PHP Patrons de conception : Poids mouche en Python Patrons de conception : Poids mouche en Ruby Patrons de conception : Poids mouche en Swift Patrons de conception : Poids mouche en TypeScript Patrons de conception : Poids mouche en Go