Flyweight pattern

Definition

Use sharing to support large numbers of fine-grained objects efficiently.

• Split heavy objects into what can be shared (flyweight / template / intrinsic data) and what to be configured (context / extrinsic data)
• The heavy object can be generated on the fly from the flyweight object and the context
• Reduce the memory cost of working with large numbers of very small objects

Flyweight vs Singleton

• flyweight pattern is acting like a common template that can be configured as per the need
• singleton pattern allows to reuse an existing object

Multithreading

Same problem and remedy as the Singleton pattern.

Exemple

User.cs

public class User { public string Name { get; set; } public override string ToString() => $"Simple user: {Name}"; }

Administrator.cs

public class Administrator : User { public override string ToString() => $"Admin user: {Name}"; }

UserFactory.cs

public class UserFactory { IDictionary<UserType, User> userTemplatesByUserType = new Dictionary<UserType, User>(); public User GetUserFromFactory(UserType userType) { User userTemplate = null; if (userTemplatesByUserType.ContainsKey(userType)) { userTemplate = userTemplatesByUserType[userType]; } else { switch (userType) { case UserType.User: userTemplate = new User(); userTemplatesByUserType.Add(UserType.User, userTemplate); break; case UserType.Administrator: userTemplate = new Administrator(); userTemplatesByUserType.Add(UserType.Administrator, userTemplate); break; case UserType.Guest: userTemplate = new Guest(); userTemplatesByUserType.Add(UserType.Guest, userTemplate); break; default: throw new Exception($"Unknown user type {userType}."); } } return userTemplate; } }

var userFactory = new UserFactory(); var user = userFactory.GetUserFromFactory(UserType.User); user.Name = "Nicolas"; Console.WriteLine(user); for (var i = 0; i < 10; i++) { // call only once the Administrator ctor then reuse the instance user = userFactory.GetUserFromFactory(UserType.Administrator); user.Name = $"Admin{i}"; Console.WriteLine(user); }