How to prevent ambiguity in C++ function templates?

To prevent ambiguity in C function templates, solutions include: explicitly specifying template parameters, by specifying a type parameter list in the function call. Use auxiliary templates to simplify the call when the function template has many parameters. This is achieved by creating an auxiliary template that accepts different types of parameters and using this template to simplify the call.

How to prevent ambiguity in C function templates

What is ambiguity in function templates?

Function template is a powerful C feature that allows us to define common functions for different types of parameters. However, ambiguity can arise when multiple function templates match a given function call. This will produce an error at compile time because it cannot determine which template to use.

Solution: Explicitly specify template parameters

To prevent ambiguity, we can explicitly specify the template parameters to be used. This is done by specifying the type parameter list in the function call.

Practical case:

template 
void print(T value) {
  std::cout << value << std::endl;
}

template 
void print(T* ptr) {
  std::cout << *ptr << std::endl;
}

int main() {
  int a = 10;
  int* b = &a;

  // 调用 print()，显式指定参数类型以避免二义性
  print(a);  // 打印 a 的值
  print(b); // 打印 b 指向的值
}

In this example, if the parameter type is not explicitly specified, the compiler will not be able to determine which function template to use (print( int) or print(int*)). By making the type explicit, we eliminate ambiguity and ensure the correct function is called.

Using Auxiliary Templates

If a function template has many parameters or type parameters, it can be cumbersome to specify all parameters explicitly. In this case, we can use helper templates to simplify the call.

Practical case:

template 
void print(T a, U b) {
  std::cout << a << " " << b << std::endl;
}

template 
void print(T value) {
  print(value, value);
}

int main() {
  int a = 10;
  double b = 3.14;

  // 使用辅助模板简化调用
  print(a, b);  // 打印 a 和 b 的值
  print(a);    // 自动调用辅助模板，打印 a 的值两次
}

We created an auxiliary template print(T, U), which accepts two different types of parameters. We then use this helper template to simplify calling the print(T) function. This removes ambiguity and makes the code cleaner.

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