Flyweight

Context: Use sharing to support large numbers of fine‑grained objects efficiently.

public class Flyweight
{
    private string _sharedState;
    public Flyweight(string state) => _sharedState = state;
    public void Operation(string uniqueState) => Console.WriteLine($"{_sharedState} + {uniqueState}");
}

public class FlyweightFactory
{
    private Dictionary<string, Flyweight> _flyweights = new();
    public Flyweight GetFlyweight(string key)
    {
        if (!_flyweights.ContainsKey(key))
            _flyweights[key] = new Flyweight(key);
        return _flyweights[key];
    }
}

Real-world usage example

Text rendering: Each character in a document can share a Character flyweight with intrinsic state (font, size, style). The extrinsic state (position) is passed when drawing.

Example: In .NET, string interning is a flyweight: identical string literals share the same memory. Also, Int32 caching in -128 to 127 range.

Related sections

• 5.2 Structural patterns
• 5.2.6 Composite
• 5.3 Behavioural patterns