#include <iostream>
#include <memory>

using namespace std;

class CPU {
public:
    string type;
    CPU(string s) {
        type = s;
    }
};

class Memory {
public:
    string type;
    Memory(string s) {
        type = s;
    }
};

class Computer {
    unique_ptr<CPU> cpu;
    unique_ptr<Memory> mem;

    friend class Builder;
public:
    void show() {
        cout << "CPU:    " << cpu->type << endl
             << "Memory: " << mem->type << endl;
    }
};

class Builder {
public:
    unique_ptr<Computer> c;
    Builder() {
        c = make_unique<Computer>();
    }

    // Method chaining
    Builder& set_cpu(string s) {
        c->cpu = make_unique<CPU>(s);
        return *this;
    }

    Builder& set_mem(string s) {
        c->mem = make_unique<Memory>(s);
        return *this;
    }

    unique_ptr<Computer> build() {
        // You can check if the computer is valid here.
        return move(c);
    }
};


int main() {
    Builder b;
    // You can pack `b.set().set()...build()` into a Director.
    auto c = b
        .set_cpu("Intel")
        .set_mem("Samsung")
        .build();
    c->show();
}