Simple Envelope/Letter Pattern

envelope.cpp

#include <iostream>
#include <memory>

using namespace std;

class Real;
class Integer;

class Number {
    friend Real;
    friend Integer;
public:
    Number() {}

    virtual Number add(const Number &n) const;
    virtual Number realAdd(const Number &) const;
    virtual Number intAdd(const Number& n) const;
    virtual void print() const;

    static Number makeReal(float r);
    static Number makeInt(int v);
protected:
    unique_ptr<Number> rep;
};

class Real : public Number {
    friend Integer;
    friend Number;

    float val;

    Real(float r) : val(r) {}
    virtual Number add(const Number &n) const;
    virtual Number realAdd(const Number &) const;
    virtual Number intAdd(const Number& n) const;
    virtual void print() const;
};

class Integer : public Number {
    friend Real;
    friend Number;

    int val;
    Integer(int n) : val(n) {}
    virtual Number add(const Number &n) const;
    virtual Number realAdd(const Number &) const;
    virtual Number intAdd(const Number& n) const;
    virtual void print() const;
};

Number Number::add(const Number& n) const {
    return rep->add(n);
}

Number Number::realAdd(const Number& n) const {
    return rep->realAdd(n);
}

Number Number::intAdd(const Number& n) const {
    return rep->intAdd(n);
}

Number Number::makeReal(float f) {
    Number n;
    n.rep.reset(new Real(f));
    return n;
}

Number Number::makeInt(int v) {
    Number n;
    n.rep.reset(new Integer(v));
    return n;
}

void Number::print() const {
    rep->print();
}

Number Real::add(const Number& n) const {
    return n.realAdd(*this);
}

Number Real::realAdd(const Number& n) const {
    const Real *rn = dynamic_cast<const Real *>(&n);
    return Number::makeReal(this->val + rn->val);
}

Number Real::intAdd(const Number& n) const {
    const Integer *it = dynamic_cast<const Integer *>(&n);
    return Number::makeReal(this->val+ it->val);
}

void Real::print() const {
    cout << "R(" << val << ")";
}

Number Integer::add(const Number& n) const {
    return n.intAdd(*this);
}

Number Integer::intAdd(const Number& n) const {
    const Integer *it = dynamic_cast<const Integer *>(&n);
    return Number::makeInt(this->val+ it->val);
}

Number Integer::realAdd(const Number& n) const {
    const Real *rn = dynamic_cast<const Real *>(&n);
    return Number::makeReal(this->val + rn->val);
}

void Integer::print() const { 
    cout << "I(" << val << ")";
}

void print_sum(Number& n1, Number& n2) {
    n1.print(); cout << " + "; n2.print();
    cout << " = "; n1.add(n2).print();
    cout << endl;
}

int main(void) {
    Number i1 = Number::makeInt(5);
    Number i2 = Number::makeInt(11);
    Number r1 = Number::makeReal(3.14);
    Number r2 = Number::makeReal(0.5);

    print_sum(i1, i2);
    print_sum(i1, r1);
    print_sum(r2, i1);
    print_sum(r1, r2);

    return 0;
}