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Flyweight

Overview​

Share common state between many objects to reduce memory usage.

When to use​

  • You have many similar objects with small variations.
  • Memory usage is a concern.

Java example​

class Glyph {
    private final String font;
    Glyph(String font) { this.font = font; }
    String render(String text) { return font + ":" + text; }
}

class GlyphFactory {
    private final Map<String, Glyph> cache = new HashMap<>();
    Glyph get(String font) {
        return cache.computeIfAbsent(font, Glyph::new);
    }
}

TypeScript example​

class Glyph {
  constructor(private font: string) {}
  render(text: string): string {
    return `${this.font}:${text}`;
  }
}

class GlyphFactory {
  private cache = new Map<string, Glyph>();
  get(font: string): Glyph {
    if (!this.cache.has(font)) {
      this.cache.set(font, new Glyph(font));
    }
    return this.cache.get(font)!;
  }
}

Pros and cons​

Pros:

  • Reduces memory usage.
  • Improves performance for large sets.

Cons:

  • Adds complexity and indirection.
  • Requires careful separation of shared vs unique state.

Common pitfalls​

  • Sharing mutable state across instances.
  • Over-optimizing when object counts are small.