C++ for Scientists - Technische Universität Dresden

7.5. FROM MONOMORPHIC TO POLYMORPHIC BEHAVIOR 217
Parametric Polymorphism
Parametric polymorphism was the first type of polymorphism developed, and first identified by
Christopher Strachey in 1967. It was also the first type of polymorphism to appear in an actual
programming language, ML in 1976. It exists in C++, Standard ML, Haskell, and others. The
term static polymorphism is often found.
In C++, this type of polymorphism can be used via templates and also lets a value have more
than one type. Inside
template double function(T param) {..}
param can have any type that can be substituted inside function to render compilable code.
This is called implicit interface in contrast to a base class’s explicit interface. It achieves the
same goal of polymorphism - writing code that operates on multiple types but in a very different
way.
To tie up to the dynamic polymorphic by example, the same example as in the static polymorphic
world is used through function templates:
#include
class topology
{
// ... temp class
};
class structured vertex
{
public:
structured vertex(int id, topology∗ topo) : id(id), topo(topo) {}
bool equal(const structured vertex& ve) const
{
return id == ve.id && topo == ve.topo;
}
protected:
int id;
topology∗ topo;
};
class unstructured vertex
{
public:
unstructured vertex(int handle, topology∗ topo, int segment) : handle(handle), segment(segment), topo(topo) {}
bool equal(const unstructured vertex& ve) const
{
return handle == ve.handle && topo == ve.topo && segment == ve.segment;
}