Re: [Boost-Users] Re: Which doorway

From: Douglas Gregor (gregod_at_[hidden])
Date: 2002-12-10 08:56:34

On Tuesday 10 December 2002 04:48 am, Malcolm Smith wrote:
> I read Boost.Function info and it sounds like part of the solution.
>
> Is there a way of associating a key with a container of *different*
> boost.Function's ?

Not directly. How are you planning to invoke functions in this map? You gave 
the example:

  // I know this is not valid code but it explains what I'm after
  typedef std::map<int, *pf(...)> StateFunctions;

  void Method1(void);
  int Method2(TCustomClass &MyClass);

  StateFunctions[1] = Method1;
  StateFunctions[2] = Method2;

My question is: do you really want the parameter lists to be different for 
StateFunctions[1] and StateFunctions[2], meaning that when calling you might 
need something like:

foo = StateFunctions[x];
if (foo has arity zero)
  foo();
else if (foo has arity one with type TCustomClass)
  foo(herClass);
else if (...)
  etc. etc.

?

Or are all the parameters to the functors known when they are put into the 
StateFunctions map? Then what you really want is something that achieves the 
desired effect:

  StateFunctions[1] = Method1;
  StateFunctions[2] = something that calls Method2 with parameter herClass

If it's the latter case, you've run into the classic Boost.Bind/Boost.Function 
(or Boost.Lambda/Boost.Function, if your compiler can handle it) scenario :)

Then you want:

  typedef std::map<int, boost::function<void()> > StateFunctions;
  
  StateFunctions[1] = &Method1;
  StateFunctions[2] = boost::bind(&Method2, boost::ref(&herClass));

  int x = something();
  StateFunctions[x](); // call the appropriate state function

If it's the former case (different parameter lists), then there's no direct 
"Boost way" to do this that I know of.

        Doug