Question

I already know the basics about functors, how they are created and so on. I now have a specific code that would probably benefit from being converted to functors:

It’s about a console input. If the user enters text and presses enter than it tries to execute the entered text as a command. Currently the available commands are stored in a std::map<std::string, (void*)(std::string)> where map.first is the name of the command and map.second is the pointer to a function containing the code for this command.

If I now convert this to functors, what would be the best way to do so? Would I simply replace the function pointer by the actual functor objects? Or would remove the map and simply call the functor with the command string (commandFunctor("command"))?
If the second: What would the best way such a functor should look like? Should I then only create ONE functor class and in it’s operator() place a if-else-if-else… checking for the commands and store the code into it?

Or should I create a new functor class for each command and call the functor that corresponds to this command?

So, in short: User enters command. Command is looked up. If comnmand exists then execute its code. How to do this in the most efficietly way with functors?

Answer 1

I would suggest using a std::map<std::string, boost::function<void(std::string)> >. Or, if you have access to a C++0x standard library, you can use std::function instead of boost::function.

A boost/std::function is a callable object that can store anything that is callable with the function type you specify. So the user can give you a function pointer, a functor of a type that they create, or even a boost/std::bind object that does function composition.