What are the rules for template specialization in C++ generic programming?

Template specialization allows specific implementations to be provided for specific types. The rules include: When an exact match specialization exists, use that specialization. This specialization is used when a partial match specialization exists. When no specialization exists, the main template is used. Full specialization takes precedence over partial specialization. Full specializations can be overloaded, but partial specializations and master templates cannot.

Template specialization rules in C++ generic programming

Template specializationallows us to A class or function provides a specific implementation rather than applying it to all types. This provides greater flexibility, efficiency, and readability.

Rules:

• If there is an explicit specialization that exactly matches a template parameter, the compiler will use that specialization.
• If an exact matching specialization does not exist, the compiler will use a partial specialization (only some of the template parameters are specified).
• If no full or partial specialization exists, the compiler uses the main template (without any template parameters specified).
• Full specialization takes precedence over partial specialization.
• Multiple full specializations can be overloaded, but partial specializations and the main template cannot be overloaded.

Practical example:

Consider the following template function for exchanging two elements:

template<typename T>
void swap(T& a, T& b) {
  T temp = a;
  a = b;
  b = temp;
}

We can create for specific types A full specialization, such as int:

template<>
void swap(int& a, int& b) {
  a ^= b;
  b ^= a;
  a ^= b;
}

When we call swap, the compiler chooses the best-matching specialization based on the argument type passed in:

int x = 1, y = 2;
// 调用完全特化的 swap 函数
swap(x, y); // x = 2, y = 1

Additional rules:

• Template specializations may accept default template parameter values.
• Specializations can be further specialized to form specialization hierarchies.
• Specialization can be applied to class and function templates.

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