Flyweight
Intent
Fits more objects into RAM by sharing common state between many objects.
Problem
A particle system with millions of particles runs out of memory because each stores its own sprite.
Solution
Split intrinsic (shared, immutable) state from extrinsic (per-use) state and share the intrinsic part.
Real-world analogy
Think of it like this
A game forest: thousands of trees share a handful of tree models. Only each tree's position and size are stored separately.
Structure
Hover or tap a numbered role to highlight it in the diagram.
- 1Flyweight — Flyweight stores the intrinsic state shared between many objects.
- 2Context — Context holds the extrinsic, unique state and pairs it with a flyweight.
- 3FlyweightFactory — Flyweight Factory manages a pool and returns an existing flyweight when one matches.
- 4Client — Client calculates or stores the extrinsic state.
Code example
A C++ code sample for Flyweight is coming soon. Factory Method, Singleton, Decorator, Observer and Strategy already have code in all six languages.
Applicability
Use Flyweight when the program must support huge numbers of similar objects and RAM is tight.
Pros and cons
Pros
- Large memory savings
Cons
- Trades RAM for CPU
- Code becomes more complicated
Check yourself
Check yourself
A text editor renders millions of characters, and the glyph data is identical for most of them.
Saved in this browser only. Part of Structural patterns (0/7).