CSC 324: Assignment 3 clarifications

These clarafications and announcements were originally posted on the assignments page.

• The solutions to this assignment are short! If you find yourself writing a lot of code, stop and rethink what you're doing. Our solutions are about 8 lines each for throwing and each function and class for mimic (main() is slightly longer, but similar to test()). If your solutions are significantly longer (i.e., more than twice as long), there's probably a better way.
• Hint: for Q2, start by getting test() working. You'll need to write Special, chop and choose.
• Example: A few people have asked for examples of operator<. Here's a very simple example:

    class myint {
    private:
      int val;
    public:
      myint(int x) { val = x; }   // constructor
      bool operator< (const myint& other) const {
        return val < other.val;
      }
    };
    

  The & says pass by reference instead of the default pass by value (thus avoiding creating a copy of the object). The const keyword promises that we won't change the value of the object being passed. Since every method in a class needs to know which instance it's being called from, each method receives an implicit this pointer. The second const (in the strange place) promises we won't change the object that this is pointing to.
• Some students are getting strange errors when declaring their chop function. Something like this:

     mimic.cc:30: syntax error before `,' token
     mimic.cc: In function `int main()':
     mimic.cc:65: no matching function for call to `chop( ...
    

  Why? chop takes an iterator, which is defined inside a class, so the type name is of the form T::A. Now this could be a type name (the type A declared inside T) or an expression in C++ (the :: is the scope operator). But the parser needs to decide before it analyzes the semantics, so it decides "it's an expression," which is wrong.
  Solution: Convince the parser it's a type name by prefacing it with the keyword typename. For example,

     int f(typename T::A x) { ... }