Polymorphism and Iterators

[pcannons]

Hello everybody,

I have a practice exam for which we don't get solutions for and wanted to see if someone could try answering one of the questions. Thank you for your time!

The question is:

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Polymorphism and Iterators
Consider the public interfaces of the following polymorphic container and associated iterator:

class Object {
public:
  virtual Object *clone() = 0;
  virtual ~Object();
};

class Bag {
  ...
public:
  void insert(Object *o); // REQ: o non-NULL
                          // EFF: inserts o into Bag
  void remove(Object *o); // EFF: removes o if present
  // Also has: ctor, copy ctor, dtor, and assign op
};

class iterInvalid {};

class BagIter {
  ...
public:
  Object *next(); // If valid, next object or NULL if done
                  // If invalid, throws iterInvalid
  BagIter(Bag &b);
};

Use these abstractions to write the following function:

template <typename T>
void removeAll(Bag &b, bool (*pred)(T *t));
// REQUIRES: T is a subtype of Object.
//           pred returns false when t is NULL
// EFFECTS: Removes all elements of b for which
//          pred(elt) returns true. 

----------------------------------------------------------

[kooth]

So what did you write?

[webJose]

The function should create an iterator for the passed bag object and then use it in a while loop. Inside the while loop, the predicate is invoked and its result tested. If it returns true, then the item is removed from the bag.