Partially reification of command

Static diagram :

Strong points :

1. 1. Extensibility
   1. 1.1 Addition or removal of a command does not need code modification
   2. 1.2 Commands' protocol factorization
2. 2. Uniform protocol
   1. 2.1 Unique access point for the command execution
3. 3. Recording facilities
   1. 3.1 Facilities in command recording

Spoiled pattern instantiations on different problems

Problem 1 :

Name :

Action encapsulation

Problem wording :

In order to animate lights during a show, a light console is used to switch on or off lights or devices (such as a smoke machine). The memorization of ignition or extinction sequences is important to the dynamism of the show. So model the possibility for a light console to chain actions on lights or a smoke machine.

Optimal solution :

Static diagram :

A classical instantiation of the pattern.

Alternative solution :

Static diagram :

This solution grants all the management to the System class but separates the real operation in different classes. So, the solution is valid, but imposes a lot of communications between the System class and the operations classes. Moreover, System does not memorize the operation but an identifier from OperationType. So, the System class must test all the identifiers during the computeOperation that is problematic if there are a lot of operations.