functors and object inheritance

A brief outline: I have a base class that builds some data objects. I then have a child class that inherits all the public methods and pointers to objects from the base class.

In that child class, I want to construct a functor (as a struct) to use in a for_each loop. My problem is that in the functor operator, I get an error when trying to access o开发者_如何学Pythonbjects.

Abbreviated example:

class Child  : public BaseClass {
  Child(DataSource& in_data): Base(in_data){};

  struct foo {
    double operator() (int x){  
        double y = in_data.some_function(x);
        // do stuff
    }            
  };
}

error: not able to access in_data.some_function.

Ideas?

Nested classes don't have visibility of members of their enclosing class (they're like static nested classes in Java).

If you want foo to access in_data, you will need to provide it a reference explicitly. So in foo's constructor, either have it take a reference to a DataSource, or a reference to a Child (and pass *this).

Your foo doesn't know about DataSource.

consider this

struct foo
{
   DataSource& ds;
   foo(DataSource& a) :ds(a) {}

   double operator() (int x)
   {
     double y = ds.in_data.some_function(x);
     .....
   }
};

You have to create foo by giving it a DataSource to refer to.