Bridge and Flyweight in Brief

Two less common structural patterns

Bridge separates an abstraction from its implementation so the two can vary independently. If you have notification types (alert, reminder, digest) and channels (email, SMS, push), subclassing every combination gives types x channels classes; a Bridge gives each notification a reference to a channel instead, so you add either dimension without touching the other. It is composition over inheritance applied to two axes. Flyweight saves memory when you have very many similar objects by sharing their common, immutable (intrinsic) state and passing the varying (extrinsic) state in from outside: for example, millions of map markers sharing a handful of icon objects, or characters in a text editor sharing glyph data. Flyweight is a performance optimisation; use it only when profiling shows memory is the problem.

Bridge and Flyweight sketches

Two independent dimensions, and a shared icon cache.

// Bridge: notification kinds x delivery channels
interface Channel { deliver(to: string, title: string, body: string): Promise<void>; }

abstract class Notification {
  constructor(protected channel: Channel) {}
  abstract send(to: string): Promise<void>;
}
class PasswordReset extends Notification {
  send(to: string) { return this.channel.deliver(to, 'Reset your password', resetBody()); }
}
class WeeklyDigest extends Notification {
  send(to: string) { return this.channel.deliver(to, 'Your week', digestBody()); }
}
new PasswordReset(new SmsChannel()).send('+15550100');

// Flyweight: share heavy, immutable icon data across many markers
const iconCache = new Map<string, Icon>();
function getIcon(kind: string): Icon {
  let icon = iconCache.get(kind);
  if (!icon) { icon = loadIcon(kind); iconCache.set(kind, icon); }
  return icon;
}
// each marker stores only position (extrinsic) + a shared icon (intrinsic)
const markers = points.map((p) => ({ lat: p.lat, lng: p.lng, icon: getIcon(p.kind) }));

You may already use these

String interning and small-integer caches in language runtimes are flyweights, and a driver interface behind a database library is a bridge, even if nobody named them.

त्वरित जाँच: What problem does Bridge address?

• A class explosion when two dimensions of variation are combined through inheritance
• Too many network calls
• Undoing user actions
• Iterating over a tree