Template Composition

You can use (but not define) 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