Question

I read C++ Primer, and it says function template specialization is an advanced topic, but I am totally lost. Can anybody offer an example why function template specialization is important and necessary?

Why don’t function templates support partial specialization while class templates do? What’s the underlying logic?

Answer 1

Basically the idea is that you can write templates that behave in a generic way for the general case, but can still handle special cases. One example of where specialization is used is in std::vector. std::vector<bool> is a specialization that packs the bool elements such that they only use one bit per element, not one byte. std::vector<T> works like a normal dynamic array for all other types.

The more advanced use for specialization is metaprogramming. For example, here’s an example (from Wikipedia) of how to use template specialization to compute factorials at compile time.

template <int N>
struct Factorial 
{
    enum { value = N * Factorial<N - 1>::value };
};

template <>
struct Factorial<0> 
{
    enum { value = 1 };
};