Recap: Chain of Responsibility Pattern

Each handler handles or passes on, and the end of the chain needs an answer too.

Chain of Responsibility sends a request along a line of handlers until one deals with it.

Intent. Decouple a sender from its receiver by letting several objects in turn have the chance to handle the request.
Structure. Each handler holds the next; the client sends only to the first.
Changing the chain. Adding, removing or reordering handlers changes the line that builds the chain, not the sender.
Order matters. The first handler that accepts a request wins, so put the checks that must win first.
In the wild. Web framework middleware, where most links act and then call next().
The trap. A request no handler accepts falls off the end and returns nothing; end every chain with a default handler or an error.
When not. One known handler, or every request must be handled and nothing guarantees it.

← → move through sections and cards