Once<T extends Object?> class final

Lazy initialization wrapper that computes a value only once and caches it.

Once ensures expensive computations or resource allocations are performed once and reused. Perfect for implementing lazy singletons, caching results, or deferring initialization until first use.

The instance itself is callable via the call method, making usage clean and intuitive.

Example:

// Expensive computation deferred until first access
final expensiveValue = Once(() {
  print('Computing...');
  return complexCalculation();
});

final result1 = expensiveValue(); // Prints 'Computing...', computes value
final result2 = expensiveValue(); // Returns cached value (no computation)

Common use cases:

• Lazy singleton initialization
• Expensive resource loading (files, network requests)
• Heavy computations deferred to first use
• Caching configuration or expensive lookups