6.4 Template Composition

You can use templates in a nested manner. This is particularly useful when defining generic functions over generic data structures, as in the standard C++ library. For example, a template sort function may be declared over a template array class:

template <class Elem> void sort(Array<Elem>);

and defined as:

template <class Elem> void sort(Array<Elem> store)
    {int num_elems = store.GetSize();
      for (int i = 0; i < num_elems-1; i++)
          for (int j = i+1; j < num_elems; j++)
              if (store[j-1] > store[j])
                  {Elem temp = store[j];
                    store[j] = store[j-1];
                    store[j-1] = temp;}}

The preceding example defines a sort function over the predeclared Array class template objects. The next example shows the actual use of the sort function.

Array<int> int_array(100);   // construct an array of ints
sort(int_array);             // sort it