What is enable_if in C++ and can you provide examples?

What is enable_if in C++ and can you provide examples?

Enable_if is a template metaprogramming utility in C++ that allows you to conditionally enable or disable function templates based on type traits.

Can you show me a simple example of how enable_if works?

Sure! Here's a basic example:

#include <iostream>
#include <type_traits>

template <typename T>
typename std::enable_if<std::is_integral<T>::value, T>::type
add(T a, T b) {
    return a + b;
}

int main() {
    std::cout << add(5, 10); // Works, as 5 and 10 are integers
    // std::cout << add(5.5, 10.5); // This would cause a compile-time error
}

This function will only compile if T is an integral type.

What happens if I try to use enable_if with a non-integral type?

If you try to use enable_if with a non-integral type, the function template will not be instantiated, leading to a compile-time error. This is useful for enforcing type constraints.

Are there any other use cases for enable_if?

Yes, enable_if can be used for SFINAE (Substitution Failure Is Not An Error) to create more flexible and type-safe APIs, allowing for function overloads based on type properties.