State: The Rogue State (Anti)PatternThings going badly when a stateful class takes up arms against its

creator

Implement a counter

1. Count to a specified maximum value, then stop.2. Do not start counting until an initialized signal is received.3. If a reset signal is received, go back to uninitialized.4. If a clear signal is received, set the count back to 0, but only if

counting is not in progress.5. The maximum value can be changed, as long as the counter is not

already counting.

Heading off to the code now…

Advantages of Enum/GoF pattern

They explicitly express important concerns in a clear way.

Advantages of the GoF Pattern

Only variables/constants relevant to a state are available in that state

Advantages of the GoF Pattern

Easier to reason about, because determining what state the system is in, has been separated from what to do in response to various signals/messages.Specifically, class structure has replaced conditional logic.

(Single Responsibility Principle)

Advantages of the GoF Pattern

Changes largely result in adding classes/methods, as opposed to editing existing methods.

Open [for extension]/Closed [for modification] Principle

Advantages of the GoF Pattern

Code is about communication with other developers (as a fringe benefit users get to do stuff).The state pattern is easier to understand.

Addendum to last week:Program Architecture and SRP

Data Object(the business domain data)

Business Methods(only operate on data

objects, NO dependency injection)

Composing Dependencies(Manager/Handler/BL

layer)