Re: "Must instantiate controlled types at library level." Why?

["Peter C. Chapin" <pchapin@sover.net>]

Jeffrey Carter <spam@spam.com> wrote in news:NJeoc.16758$V97.5496
@newsread1.news.pas.earthlink.net:

> The call to Library_Level.Op would attempt to dispatch to 
> Outer.Inner.Op, which is out of scope. The references to I in 
> Outer.Inner.Op refer to a variable that no longer exists.

Thank you for your detailed post. It was very helpful. I haven't yet 
gotten around to studying Ada's object oriented features in detail but I 
can see that the issue is related to the fact that Ada allows procedures 
to be defined inside other procedures.

Just for fun I attached an equivalent C++ program below. Interestingly, it 
seems to compile and work using three different C++ compilers. I wonder 
its behavior is technically "undefined". It seems like it probably should 
be. Perhaps I'll ask on the C++ group.

Peter

-----> cut <-----
#include <iostream>

class X {
public:
  virtual void f();
};

void X::f()
{
  std::cout << "I'm in X::f\n";
}

X *ptr;

void helper()
{
  class Y : public X {
  public:
    virtual void f() { std::cout << "I'm in Y::f\n"; }
  };

  ptr = new Y;
}

int main()
{
  helper();
  ptr->f();
  return 0;
}