Lazy Singleton (no class)

export function lazy<T>(factory: () => T): () => T {
  let cached: T | undefined;
  let initialized = false;
  return () => {
    if (!initialized) {
      cached = factory();
      initialized = true;
    }
    return cached as T;
  };
}

// Module-scoped lazy singleton — DB connection
const getDb = lazy(() => {
  console.log('Connecting to DB…');           // logged exactly once
  return new DatabaseClient(process.env.DATABASE_URL!);
});

// Anywhere in the codebase:
const db = getDb();   // first call: opens connection
const db2 = getDb();  // subsequent calls: returns the same instance