C++ Template Metaprogramming/

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Understanding Partial Specialization

Understanding Partial Specialization

Understand the details of partial specialization in this lesson.

We'll cover the following...

In the previous lesson, we explored a variant of template specialization (explicit or full specialization). In this lesson, we’ll take a closer look at partial specialization, which is the second form of template specialization.

Partial specialization

Partial specialization occurs when we specialize a primary template but only specify some of the template arguments. This means a partial specialization has both a template parameter list (which follows the template keyword) and a template argument list (which follows the template name). However, only classes can be partially specialized.

Let’s explore the following example to understand how this works:

template<typename T, int S>
struct collection
{
   void operator()()
   { std::cout << "primary template\n"; }
};
template<typename T>
struct collection<T, 10>
{
   void operator()()
   { std::cout << "partial specialization <T, 10>\n"; }
};
template<int S>
struct collection<int, S>
{
   void operator()()
   { std::cout << "partial specialization <int, S>\n"; }
};
template<typename T, int S>
struct collection<T*, S>
{
   void operator()()
   { std::cout << "partial specialization <T*, S>\n"; }
};
Partial specialization of class templates

We have a primary template called collection that has two template arguments (a type template argument and a non-type template argument), and we have three partial specializations, as follows:

  • A specialization for the non-type template argument S with the value 10

  • A specialization for the int type

  • A specialization for the pointer type T* ... ...