What are the differences between SFINAE and constexpr?

What are the differences between SFINAE and constexpr?

SFINAE (Substitution Failure Is Not An Error) is a C++ template metaprogramming technique, while constexpr is a keyword that allows functions and variables to be evaluated at compile time. SFINAE is used for template specialization, whereas constexpr is used for defining constant expressions.

Can you give an example of SFINAE in action?

Sure! Here's a simple example: You can use SFINAE to enable a function only if a type has a specific member function. For instance:

template <typename T, typename = decltype(std::declval<T>().memberFunction())>
void func(T t) {
    // This function is only enabled if T has memberFunction()
}

How does constexpr improve performance?

Using constexpr allows computations to be done at compile time, which can lead to faster runtime performance since the results are precomputed. This reduces the amount of work done during execution.

Are there any limitations to using constexpr?

Yes, constexpr has some limitations. For example, in C++11, only simple expressions could be used, but C++14 and later versions have relaxed these restrictions, allowing more complex computations. However, constexpr functions must still adhere to certain rules, like not having side effects.