How to come up with good designs?

Question

I am trying to learn and implement classes and encountered this problem of implementing nested classes. I have implemented a version of it. I wanted to ask whether you would consider it a good example for nested classes? How can we achieve the same purpose without nesting these classes?

#include<iostream>

class Stack {
    class Node {
        public:
            int data;
            Node* next;
            Node(int data, Node* next);
            ~Node();
    }* head;
    public:
        Stack();
        Stack(const Stack& s);
        void operator=(const Stack& s);
        ~Stack();
        void push(int data);
        int peek() const;
        int pop();
};

First of all your class will break if copied. You need copy constructor and assignment operator. Next, your peek function can be const. — Neil Kirk, Oct 08 '13 at 16:48
"problem of implementing nested classes" I think it'll be better idea if you ask question about this problem. — SigTerm, Oct 08 '13 at 16:53
@NeilKirk What do you mean by breaking the class? And just to confirm, that the compiler won't create the copy constructor and assignment operator because of rule of three as the constructor has been already defined? — Sumit Gera, Oct 08 '13 at 17:19
Try coping your class with some data in it and you will see. The compiler will generate default copy constructor and assignment operator which just performs a simple copy of class members. In this case, the head pointer will be copied and both stacks will refer to the same stack. — Neil Kirk, Oct 08 '13 at 20:50

SigTerm · Accepted Answer · 2013-10-08T16:58:27.467

I wanted to ask whether you would consider it a good class design?

No, because you don't need linked list to implement stack, because you don't throw exceptions, because you aren't using existing solutions (such as std::stack, std::vector or std::deque), and because your class doesn't obey rule of three.

template<typename Val> class Stack{
protected:
    typedef std::vector<Val> Data;
    Data data;     
public:
    const Val& top() const{
        if (!data.size())
            throw std::underflow_error();
        return data[data.size()-1];
    }
    void push(const Val& arg){
        data.push_back(arg);
    }
    Val pop(){
        Val result = top();
        data.pop_back();
        return result;
    }
};

this problem of implementing nested classes.

For "nested classes exercise" linked list is more suitable.

How should I go about it? What should be my approach towards it?

Write as little as possible, reuse existing solutions, and keep it simple.

Are there any good books on it?

There should be books about design patterns, but it might be too early for them. I'd suggest to just keep practicing for a while, preferably using real problems you're interested in.

"you aren't using existing solutions (such as std::stack)." That's a bit harsh. It's fine to make a new solution as a learning exercise. — Neil Kirk, Oct 08 '13 at 16:49
@NeilKirk: That's the truth, though. Reinventing the wheel is a good exercise, but it isn't really a good design. — SigTerm, Oct 08 '13 at 16:51

score 0 · Answer 2 · edited May 23 '17 at 10:31

I personally think nested classes can be a good design choice, but you will need to weigh out if they fit your current situation. In your specific case, it seems fine to me to implement it as a nested class. I would think it is important, that the nested class only has little functionality and is specific to the class that it is nested in.

For further discussion look in this thread: Pros and cons of using nested C++ classes and enumerations?

Hope this helps :)

edit: A different approach would be to implement it as a flat class structure and don't nest the classes. This has some advantages like the possibility for forward declarations, which can be useful for more complex structures.

How to come up with good designs?

2 Answers2