Flyweight

• Intent: Use sharing to support large numbers of fine-grained objects efficiently.
• A flyweight is a shared object th at can be used in multiple contexts simultaneously.
• Intrinsic state is stored in the flyweight; it consists of information that ‘s independent of the flyweight’s context, thereby making it sharable.
• Extrinsic state depends on and varies with the flyweight’s context and therefore can’t be shared. Client objects are responsible for passing extrinsic state to the flyweight when it needs it.

General Structure

Example

In my example the participants are represented as following:

• Flyweight: Book
• Concrete Flyweight: BookRental
• Flyweight Factory: BookFactory
• Client: Library

Pros/Cons

Pros ❤️

• It lets you save your space, which increase as more flyweights are shared.
• Storage savings are a function of several factors:
  • the reduction in the total number of instances that comes from sharing
  • the amount of intrinsic state per object
  • whether extrinsic state is computed or stored
• Sharing reduces the cost of intrinsic state, and you trade extrinsic state for computation time.

Cons 💔

• It may introduce run-time costs associated with transferring, finding, and/or computing extrinsic state, especially if it was formerly stored as intrinsic state.