C++ function templates combined with SFINAE (type derivation fails valid)?

Function templates can be used in conjunction with SFINAE to create generic functions and adjust function behavior based on template parameter types. SFINAE allows us to control function availability based on whether template parameter type deduction fails. When used together, function templates can refine behavior based on type constraints, such as distinguishing between integer and non-integer types, excluding boolean types, etc., resulting in flexible and type-safe code.

Combination of C function templates with SFINAE

Introduction

C function templates allow us to create generics Functions, available for many different types. However, in some cases we may want to refine function behavior based on the type of template parameters. This is where SFINAE (Type Deduction Failed Efficient) comes in.

SFINAE

SFINAE is a technique that allows us to decide the availability of a function based on the presence or absence of a template parameter type. If a template argument cannot be inferred, the compiler will report a derivation failure, which we can use to control function availability.

C Combination use of function templates and SFINAE

We can extend the functionality of function templates by using SFINAE. Let's look at an example:

template <typename T>
typename std::enable_if<std::is_integral<T>::value, void>::type func(T x) {
  // Integral type-specific implementation
}

template <typename T>
typename std::enable_if<!std::is_integral<T>::value, void>::type func(T x) {
  // Non-integral type-specific implementation
}

In this example, we create a function template func and select different function signatures based on the type of the template parameter T . Using std::enable_if, we create two nested functions that are only available when specific type constraints are met. For integer types, the first function will be called, and for non-integer types, the second function will be called.

Practical Case

The following is a practical case of using C function templates with SFINAE:

// 实现求平方和的函数模板
template <typename T>
auto sum_of_squares(const std::vector<T>& v) {
  typename std::enable_if<!std::is_same<T, bool>::value, decltype(v[0]*v[0])>::type result = T{};

  for (const auto& elem : v)
    result += elem * elem;

  return result;
}

In this case, we created a Function template sum_of_squares, which will find the sum of the squares of all elements in the vector. Using SFINAE, we exclude the Boolean type because it does not support square operations.

Conclusion

The combined use of C function templates and SFINAE provides a powerful tool that can help us create flexible and type-safe generic code. By leveraging template parameter types, we can refine function behavior at runtime based on type constraints. This allows us to write efficient and scalable code.

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