Demonstrate how a dynamic type system might be implemented

dynamic.cc

// File: dynamic.cc
// Purpose: Demonstrate how a dynamic type system might be implemented
// Author: Fares A. Bakhit
// Date: May 8th, 2024
// License: Zero Clause BSD (https://spdx.org/licenses/0BSD.html)

#include <cstdint>
#include <iostream>
using namespace std;

// A dynamically-typed variable
struct var {
    enum class type {
        integer,
        character,
    };

    var(const int32_t& val)
        : m_ty(type::integer)
    {
        m_val = malloc(sizeof(int32_t));
        *(int32_t*)m_val = val;
    }

    void operator=(const int32_t& val)
    {
        if (m_ty == type::integer) {
            *(int32_t*)m_val = val;
            return;
        }
        m_ty = type::integer;
        free(m_val);
        m_val = malloc(sizeof(int32_t));
        *(int32_t*)m_val = val;
    }

    var(const char& val)
        : m_ty(type::character)
    {
        m_val = malloc(sizeof(char));
        *(int32_t*)m_val = val;
    }

    void operator=(const char& val)
    {
        if (m_ty == type::character) {
            *(char*)m_val = val;
            return;
        }
        m_ty = type::character;
        free(m_val);
        m_val = malloc(sizeof(char));
        *(char*)m_val = val;
    }

    ~var()
    {
        free(m_val);
    }

    void operator+=(int32_t val)
    {
        switch (m_ty) {
        case type::integer:
            *(int*)(m_val) += val;
            break;
        default:
            cerr << "error: invalid type\n";
            exit(1);
        }
    }

    type m_ty;
    void* m_val = nullptr;
};

ostream& operator<<(ostream& os, const var& v)
{
    switch (v.m_ty) {
    case var::type::integer:
        os << *(int32_t*)(v.m_val);
        break;
    case var::type::character:
        os << *(char*)(v.m_val);
        break;
    }
    return os;
}

int main()
{
    // a character...
    var mypain = 'F';
    //mypain += 32;  // this would error at runtime
    cout << "mypain=" << mypain << '\n';
    // is now an integer!
    mypain = 3;
    mypain += 2;
    cout << "mypain=" << mypain << '\n';
}