constrexpr exponential function

exp.cpp

// Adapted from an interview question that does the same with templates
// The goal was just to make the logic easier to understand with recent C++ features
// Don't use it in real-life LOL.
//
// It needs (1) a small wrapper to make the API cleaner (2) templates to work with any type...
// and in real-life you'll want more precision/speed/range/vectorization..........
//
// To check it's indeed compile time: https://godbolt.org -std=c++17

#include <iostream>
#include <utility>

constexpr std::pair<double, double> exp(double x, int n) {
    if (n==0)
        return std::pair<double, double>(1, 1);
    return std::pair<double, double>(
        exp(x, n-1).first * x / n,
        exp(x, n-1).second + exp(x, n).first
    );
}

int main() {
    constexpr double x = 3;
    constexpr int n = 10;
    std::cout << exp(x, n).second << std::endl;
}