Advanced C++ Topics

Nested Classes and Name Spaces

In the standard library, the iterator class is nested inside the list class.
```
list<string>::iterator pos = staff.begin();
```
The reason is so several different implementations (for vectors, lists, maps, and sets) can all share the same name (iterator), but have different implementations.
```
vector<double>::iterator p = a.begin();
list<string>::iterator q = b.begin();
```
To nest a class inside another, first declare the nested class inside the outer class.
```
class List
{
   ...
   class Iterator;
   ...
};
```