Other C++20 Enhancements

In C++20, several enhancements were made to the constexpr feature, including the ability to modify members of a union and the inclusion of certain language constructs like dynamic_cast, typeid, and inlined assembly within constexpr functions.

Modifying members of a union in constexpr

In earlier versions of C++, modifying a member of a union within a constexpr context was not allowed. However, starting from C++20, it became possible. Here's an example that demonstrates this:

#include <iostream>

union MyUnion {
    int i;
    float f;
};

constexpr int modifyUnionMember(int value) {
    MyUnion u;
    u.i = value;
    return u.f;  // Modify the float member
}

int main() {
    constexpr int modifiedValue = modifyUnionMember(42);
    std::cout << "Modified value: " << modifiedValue << std::endl;
    return 0;
}

dynamic_cast and typeid within constexpr

C++20 also introduced the ability to use dynamic_cast and typeid operators within constexpr functions. This allows for dynamic type checks and type information retrieval during compile-time evaluation. Here's an example:

#include <iostream>
#include <typeinfo>

struct Base {
    virtual ~Base() {}
};

struct Derived : Base {};

constexpr bool isDerivedFromBase(const Base* obj) {
    return dynamic_cast<const Derived*>(obj) != nullptr;
}

constexpr const std::type_info& getTypeInfo(const Base* obj) {
    return typeid(*obj);
}

int main() {
    constexpr Base* basePtr = new Derived();
    constexpr bool isDerived = isDerivedFromBase(basePtr);
    constexpr const std::type_info& typeInfo = getTypeInfo(basePtr);

    std::cout << "Is Derived from Base? " << isDerived << std::endl;
    std::cout << "Type info: " << typeInfo.name() << std::endl;

    delete basePtr;
    return 0;
}

Inlined assembly within constexpr

C++20 also allows the use of inlined assembly within constexpr functions, enabling low-level operations during compile-time evaluation. Here's an example:

#include <iostream>

constexpr int addNumbersInlineAssembly(int a, int b) {
    int result;
    asm("add %[a], %[b];"
        : [result] "=r" (result)
        : [a] "r" (a), [b] "r" (b)
    );
    return result;
}

int main() {
    constexpr int sum = addNumbersInlineAssembly(10, 20);
    std::cout << "Sum: " << sum << std::