Re: SetMode(Enum) vs. SetModeA(), SetModeB()...

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 4 May 2007 10:11:03 CST

Message-ID:

<uDH_h.26182$uJ5.444115@twister2.libero.it>

chase.bradford@saic.com ha scritto:

When writing a class that can be in exactly one of many modes, what
interface should I provide for changing the mode?

As proposed by another poster, I would consider the State pattern.

Two techniques come to mind for this.
1) Define a Mode enumerated type, with a method SetMode that takes a
Mode argument and switches across them.
2) For each mode, have a no argument method to change into that mode.

I can think of some cases where technique 1 is preferred, for
instance, when the mode needs to be stored as a variable and restored
later. This could occur in the case of a stack, where changing modes
pushes current modes onto a stack, then unwinding could be performed
with SetMode( stack.top() ).

You easily achieve the same even in approach 2, by using a stack of
pointer-to-member-functions. That is:

     std::stack<void (MyClass::*)()> modes;
     modes.push(&MyClass::SetModeA);
     (obj.*modes.top())(); // set obj in mode "A"
     (this->*modes.top())(); // set *this in mode "A"

HTH,

Ganesh

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