Partial specialization allows template classes (not functions) to define specialized versions for particular template parameter patterns. For example, a template class can have a separate specialization for pointer types or for template types, enabling different implementations for different type categories.

Use partial specialization to provide optimized or behavior-specific implementations for certain template argument patterns.

This example shows partial specialization for pointers and containers.

// compile: g++ -std=c++17 -o partial partial.cpp
// run: ./partial
// description: partial specialization customizes templates for parameter patterns
 
#include <iostream>
#include <vector>
 
// Primary template
template <typename T>
class Printer {
public:
    void print(const T& x) { std::cout << "Generic\n"; }
};
 
// Partial specialization for pointers
template <typename T>
class Printer<T*> {
public:
    void print(T* const& x) { std::cout << "Pointer specialization\n"; }
};
 
// Partial specialization for containers
template <typename T>
class Printer<std::vector<T>> {
public:
    void print(const std::vector<T>& x) { std::cout << "Vector specialization\n"; }
};
 
int main() {
    Printer<int> p1;
    p1.print(42);
 
    Printer<int*> p2;
    int x = 10;
    p2.print(&x);
 
    Printer<std::vector<int>> p3;
    std::vector<int> v{1, 2, 3};
    p3.print(v);
 
    return 0;
}