Question

I am looking into working code from Game AI by example book and there is a part I do not understand.

There is

template <class node_type, class edge_type>   
class SparseGraph                                 
{ ... };

and

int SparseGraph<node_type, edge_type>::AddNode(node_type node)
{
  if (node.Index() < (int)m_Nodes.size())
...
}    

How can be node.Index()called?

There also is class

class GraphNode
{  
public:
...   
  int  Index()const{return m_iIndex;}
....
};   

and graph is created with this class

typedef SparseGraph<GraphNode, GraphEdge> NavGraph;
NavGraph * m_pGraph;

so I understand what node.Index() does, BUT
how can I call node.Index() while there is no guarantee that node_type is GraphNode.

what if node_type is not GraphNode??

Hope you understand my question.

Answer 1

If node_type is not GraphNode, then your compiler will smack you and throw an error. However, if your class depends on the Index function, then you should document it as a requirement and any replacement for GraphNode must provide it, probably with some expected semantics.