How do I use enable_if in C++?

What is enable_if in C++ and how do I use it?

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

Can you give me an example of how to use enable_if?

Sure! Here's a simple example:

#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() {
    int result = add(5, 10); // Works
    // double result2 = add(5.0, 10.0); // This will cause a compile-time error
}

This function add will only compile for integral types.

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

If you try to use add with a non-integral type, like double, it will result in a compile-time error, preventing the code from compiling.

Are there any alternatives to enable_if?

Yes, you can use std::conditional or concepts (in C++20) as alternatives for more readable and expressive type constraints.