Constexpr Config

constexpr names a value that can be used at compile time, while ordinary variables still drive runtime decisions.

constexpr_config.cpp

#include <array>
#include <iostream>

int main() {
    constexpr int freeLimit = 3;
    int used = ;

    std::array<int, freeLimit> included{1, 2, 3};
    bool overLimit = used > freeLimit;

    std::cout << "freeLimit=" << freeLimit << std::endl;
    std::cout << "includedSlots=" << included.size() << std::endl;
    std::cout << "used=" << used << std::endl;
    std::cout << "overLimit=" << overLimit << std::endl;
    return 0;
}

#include <array>
#include <iostream>

int main() {
    constexpr int freeLimit = 3;
    int used = ;

    std::array<int, freeLimit> included{1, 2, 3};
    bool overLimit = used > freeLimit;

    std::cout << "freeLimit=" << freeLimit << std::endl;
    std::cout << "includedSlots=" << included.size() << std::endl;
    std::cout << "used=" << used << std::endl;
    std::cout << "overLimit=" << overLimit << std::endl;
    return 0;
}

#include <array>
#include <iostream>

int main() {
    constexpr int freeLimit = 3;
    int used = ;

    std::array<int, freeLimit> included{1, 2, 3};
    bool overLimit = used > freeLimit;

    std::cout << "freeLimit=" << freeLimit << std::endl;
    std::cout << "includedSlots=" << included.size() << std::endl;
    std::cout << "used=" << used << std::endl;
    std::cout << "overLimit=" << overLimit << std::endl;
    return 0;
}

constexpr A `constexpr` variable is known during compilation when its initializer is also a constant expression.