What are some examples of constexpr templates in C++20?

What are some examples of constexpr templates in C++20?

C++20 introduced several enhancements to constexpr templates. For example, you can now use them in more complex scenarios, like recursive templates. Would you like to see a specific example?

Yes, please show me a recursive constexpr template example.

Sure! Here's a simple example of a constexpr template that calculates the factorial of a number:

template<int N>
constexpr int factorial() {
    return N <= 1 ? 1 : N * factorial<N - 1>();
}

You can call it like this: constexpr int result = factorial<5>(); which will evaluate to 120 at compile time.

That's great! Can you explain how it works?

Absolutely! The factorial template uses recursion to compute the factorial of N. The base case is when N is 1 or less, returning 1. For other values, it multiplies N by the factorial of N - 1, allowing it to compute the result at compile time.

Are there any limitations to using constexpr templates?

Yes, there are some limitations. For instance, you can't use dynamic memory allocation or certain runtime features within a constexpr context. However, C++20 has expanded the capabilities significantly compared to previous versions.