Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 7 | Object Oriented Design
1 struct Object { … };
2 struct RefCountPtrImpl {
3 int count;
4 Object * object;
5 };
6 struct RefCountPtr {
7 RefCountPtrImpl * pointee;
8 };
Advantages: no memory overhead because of two pointers.
Disadvantages: performance penalty because of extra level of indirection.
3. Intrusive reference counting.
1 struct Object { … };
2 struct ObjectIntrusiveReferenceCounting {
3 Object object;
4 int count;
5 };
6 struct RefCountPtr {
7 ObjectIntrusiveReferenceCounting * pointee;
8 };
Advantages: no previous disadvantages.
Disadvantages: class for intrusive reference counting should be modified.
4. Ownership list reference counting. It is an alternative for approach 1-3. For 1-3 it is only
important to determine that counter is zero—its actual value is not important. This is the
main idea of approach # 4.
All Smart-Pointers for given objects are stored in doubly-linked lists. The constructor of a
smart pointer adds the new node to a list, and the destructor removes a node from the list
and checks if the list is empty or not. If it is empty, the object is deleted.
1 struct Object { };
2 struct ListNode {
3 Object * pointee;
4 ListNode * next;
5 }
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