Why is C++ said not to support parametric polymorphism?

Question

According to the wikipedia page for Parametric Polymorphism:

Some implementations of type polymorphism are superficially similar to parametric polymorphis

Answer 1

The article you linked to explains that. The very text you quoted actually gives one example of something that sets C++'s templates apart from pure parametric polymorphism: C++ template specialisation.

It continues on this theme:

Following Christopher Strachey,^[2] parametric polymorphism may be contrasted with ad hoc polymorphism, in which a single polymorphic function can have a number of distinct and potentially heterogeneous implementations depending on the type of argument(s) to which it is applied. Thus, ad hoc polymorphism can generally only support a limited number of such distinct types, since a separate implementation has to be provided for each type.

Thus, as described, C++ templates come close to — but are not exactly — parametric polymorphism.