Page History

...

The following utility data structures are designed to handle the situation where an operation has more than 2 or more possible outcomes.  While not entirely optimal, these classes show how clever sub-classing can enable one to re-use classes in multiple situations.

• Wiki Markup* {{IUtilHostAB}} \-\- {{IUtilVisitorAB}}* :  A  IUtilHostAB -- IUtilVisitorAB :  A host-visitor set that represents a situation where there are +two+ possible outcomes.    There are two possible concrete hosts, {{UtilHostA}} and {\[UtilHostB}} and thus the {{IUtilVisitorAB}} visitor has two cases corresponding to these two hosts.

• Wiki Markup
  {{IUtilHostABC}} \-\- {{IUtilVisitorABC}} :  A host-visitor set that represents a situation where there are +three+ possible outcomes.    There are three possible concrete hosts, {{UtilHostA}}, {\[UtilHostB}} and {{UtilHostC}} and thus the {{IUtilVisitorABC}} visitor has three cases corresponding to these three hosts.

Wiki Markup{{IUtilHostABCD}} \-\- {{IUtilVisitorABCD}} :  A host-visitor set that represents a situation where there are +four+ possible outcomes.    There are four possible concrete hosts, {{UtilHostA}}, {\[UtilHostB}}, {\[UtilHostC}} and {{UtilHostD}} and thus the {{IUtilVisitorABCD}} visitor has four cases corresponding to these three hosts.
•     There are two possible concrete hosts, UtilHostA and UtilHostB and thus the IUtilVisitorAB visitor has two cases corresponding to these two hosts.
• IUtilHostABC -- IUtilVisitorABC :  A host-visitor set that represents a situation where there are three possible outcomes.    There are three possible concrete hosts, UtilHostA, UtilHostB and UtilHostC and thus the IUtilVisitorABC visitor has three cases corresponding to these three hosts.
• IUtilHostABCD -- IUtilVisitorABCD :  A host-visitor set that represents a situation where there are four possible outcomes.    There are four possible concrete hosts, UtilHostA, UtilHostB, UtilHostC and UtilHostD and thus the IUtilVisitorABCD visitor has four cases corresponding to these three hosts.

 Typically, a method returns a value of type IUtilHostAB/C/D depending on how many possibilities there are.  For instance, a single reduction pass on the Sudoku board would result in a value of IUtilHostABCD, corresponding to the 4 possible outcomes for the board: being still reducible, irreducible, solved or unsolvable.

 The caller of such a method need only to simply delegate to the returned value by having the returned value accept the proper visitor.   Suppose the method my3OutcomeMethod} has three possible outcomes, so it returns an {{IUtilHostABC object.    All we need to do is to delegate to the returned value of the method:

my3OutcomeMethod().accept(new IUtilVisitorABC() {...})

Model-View-Controller Architecture

...