On Jul 18, 4:21 pm, LarryTheSoftware...@hotmail.com wrote:
Quote:
Folks,
>
Would love some suggestions re what design patterns to use for this
situation.
>
I need to create a simple FSM. A certain login scenario will behave
differently based on the following:
>
· 1 - 3 session traits, which are already established & stay the same
for the session duration. Trait #2 is only relevant if trait #1 is a
certain value. Trait #3 is only relevant if trait #2 is a certain
value.
· 2 different sets of states - plus a third state if the 2nd statehas
a certain value.
>
All these traits & states are maintained locally in my program.
>
When I look at the possibilities in GoF & in Alexandrescu on how to
implement this, my head spins - Object factory? Abstract factory?
Functor? State pattern? Decorator? Brute force 'if' tests?:-) All of
the above? (More than one of the above I'm sure, but I'd love some
general suggestions on which pattern would make sense where.) Thank
you verrrrry much.
>
Larry Kay
Sometimes it's best not to force existing design patterns on
yourself. How about a HSM (Heierarchical State Machine). Make a
class representing each "state". These all derive from the same
abstract class, which has methods like Enter(), Leave(), and
Execute(). Each of these states has sub-states.
Then, in each subclass, you can have totally different trait
enumerations since certain traits only apply to certain states. Plus
the 3rd state can exist only as a member of the 2nd state. Etc.
Organizing state machines into heierarchies can be pretty useful in
cases like this where each state itself defines a complex set of
behavior.
