Re: Tree of maps and leaves
* 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
array.
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
{
public:
virtual ~Any() {};
virtual void execute() const = 0;
};
class Void: public Any
{
public:
virtual ~Void() {}
virtual void execute() const {};
};
class Quit: public Any
{
public:
virtual void execute() const { exitApp(); }
};
}
class UserCommandState;
typedef SomeSharedPtr<UserCommandState> UserCommandStatePtr;
typedef std::map< char, UserCommandStatePtr > KeyBindings;
class UserCommandState
{
private:
KeyBindings mySuccessorStates;
public:
virtual ~UserCommandState() {}
UserCommand const* command() const
{
static userCommand::Void const theVoidCommand;
if( userCommand::Any const* pCmd =
dynamic_cast<userCommand::Any const*>( this ) )
{
return pCmd;
}
else
{
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. :-)
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