Design patterns in the test of timeChain of responsibility

time to read 2 min | 344 words

The chain-of-responsibility pattern is a design pattern consisting of a source of command objects and a series of processing objects. Each processing object contains logic that defines the types of command objects that it can handle; the rest are passed to the next processing object in the chain. A mechanism also exists for adding new processing objects to the end of this chain.

More about this pattern.

It is actually quite common to see this pattern now-a-days using events. Something like CancelEventArgs and a CancelEventHandler to handle the FormClosing event of a Form.

We use Chain of Responsibility in RavenDB in several places, like this one:

foreach (var requestResponderLazy in currentDatabase.Value.RequestResponders)
  var requestResponder = requestResponderLazy.Value;
  if (requestResponder.WillRespond(ctx))
    var sp = Stopwatch.StartNew();
    ctx.Response.AddHeader("Temp-Request-Time", sp.ElapsedMilliseconds.ToString("#,# ms", CultureInfo.InvariantCulture));
    return requestResponder.IsUserInterfaceRequest;

Note that we have moved on the the behavioral patterns, and those tend to have withstand the test of time much better, in general.

Other places where Chain of Responsibility is used is request routing and error handling. A common approach is to also have this done by delegating, where I am handling what I can and passing on to the next object if I don’t know how to handle a request.

Recommendation: This is still a very useful pattern. One thing to note is that it is effectively an O(N) operation with respect to the number of items in the chain that you have. As usual, do not overuse, but it is a really nice pattern.

More posts in "Design patterns in the test of time" series:

  1. (21 Jan 2013) Mediator
  2. (18 Jan 2013) Iterator
  3. (17 Jan 2013) Interpreter
  4. (21 Nov 2012) Command, Redux
  5. (19 Nov 2012) Command
  6. (16 Nov 2012) Chain of responsibility
  7. (15 Nov 2012) Proxy
  8. (14 Nov 2012) Flyweight
  9. (09 Nov 2012) Façade
  10. (07 Nov 2012) Decorator
  11. (05 Nov 2012) Composite
  12. (02 Nov 2012) Bridge
  13. (01 Nov 2012) Adapter
  14. (31 Oct 2012) Singleton
  15. (29 Oct 2012) Prototype
  16. (26 Oct 2012) Factory Method
  17. (25 Oct 2012) Builder
  18. (24 Oct 2012) A modern alternative to Abstract Factory–filtered dependencies
  19. (23 Oct 2012) Abstract Factory