When should I use template specialization in C++?

Template specialization is useful in scenarios where you have a generic template, but need to provide a different implementation for certain types. Some practical examples include:

1. Optimizing performance: If you have a generic algorithm that works for most types, but can be optimized for specific types, you can create a specialized version of the template for those types.
2. Adapting to different type interfaces: When working with different types that have similar but not identical interfaces, you can use specialization to adapt the template to each type's specific interface.
3. Integrating with libraries: Libraries often provide templates that you can specialize for your own types. For example, specializing std::hash allows your type to be used with hash-based containers like std::unordered_map.
4. Enabling specific functionality: Some types may require special handling or have unique characteristics. Specialization allows you to enable specific functionality for those types within a generic context.

Here's an example of optimizing performance using specialization:

1// Generic template
2template <typename T>
3T square(T x) {
4  return x * x;
5}
6
7// Specialization for int
8template <>
9int square<int>(int x) {
10  // Optimized version for int using bit shift
11  return x << 1;
12}

In this case, the specialized version for int uses a bitwise shift operation, which can be faster than multiplication for integers.