Re: Tree of maps and leaves

"Alf P. Steinbach" <>
Tue, 03 Mar 2009 07:27:55 +0100
* Andre Majorel:

I need to store key bindings. Those are unusual in that the
"key" can in fact be a *sequence* of keystrokes (think Vim's ga,
gq, etc...).

Seems to me that a good way to store the bindings would be a
tree of associative arrays where the key is a keystroke and the
value is either a) an "action" that describes the function to
which that key sequence is bound or b) a similar associative

For example, given the following bindings :

  a action1
  b action2
  cx action3
  cy action4

... there would be two associative arrays, one containing :

  'a' => action1
  'b' => action2
  'c' => pointer-or-reference-to-whymakeitsimple

... and another, whymakeitsimple, containing :

  'x' => action3
  'y' => action4

Were this C, I'd malloc and cast my way out of it. I'm trying to
do it the STL way, however. Now, that might be slight
retardation on my part but I don't quite see how to do that with
std::map. Is some graph container from Boost the answer ?

It seems that the point of your design is to allow various information to be
associated with each initial substring of a command.

std::map is good, but to keep your design you'll have to rethink what to store.

Off the cuff:

   namespace userCommand
       class Any
           virtual ~Any() {};
           virtual void execute() const = 0;

       class Void: public Any
           virtual ~Void() {}
           virtual void execute() const {};

       class Quit: public Any
           virtual void execute() const { exitApp(); }

   class UserCommandState;
   typedef SomeSharedPtr<UserCommandState> UserCommandStatePtr;

   typedef std::map< char, UserCommandStatePtr > KeyBindings;

   class UserCommandState
       KeyBindings mySuccessorStates;

       virtual ~UserCommandState() {}

       UserCommand const* command() const
           static userCommand::Void const theVoidCommand;

           if( userCommand::Any const* pCmd =
                   dynamic_cast<userCommand::Any const*>( this ) )
               return pCmd;
               return &theVoidCommand;

       void setSuccessorFor( char key, UserCommandStatePtr state )
           mySuccessorStates[key] = state;

   class UserCommandStateQuit: public UserCommandState, public userCommand::Quit
   {} // Yup, that's all.

   int main()
       KeyBindings cmdStates;
       // Add bindings

Presumably efficiency doesn't matter for this thing.

If it matters then you may be better off using pure function pointers, avoiding
that dynamic_cast.

Cheers & hth.,

- Alf

Disclaimer: I haven't tried this. :-)

Due to hosting requirements I need visits to [].
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