Range-Based For Loop Implementation

I was interested in learning how to make my Linked List class adhere to a range-based for loop. I eventually saw a really good stackoverflow response that helped me figure out how to do it. This is my attempt at showing you how I implemented this feature with minimal lines of code. I will be speaking in context of a Linked List class.

Recall this is what the CPP documentation says about the Range-Based For Loop:

for ( range-declaration : range-expression )

loop-statement 

• range-declaration = the variable you are going to use to hold onto the node object
• range-expression = the Linked List class

What you need for your Linked List class are two things:

Two methods:

Iterator begin() { return this->first(); }
Iterator end() { return NULL; }

begin() returns the first node of your Linked List (note first() returns a class Node) and end() will return NULL to identify the end of the list.

1. An Iterator class

Notice both methods return Iterator. This is a nested class inside the Linked List:

class Iterator {
private:
    Node * _curr;
public:
    Iterator(Node * n) : _curr(n) {}
    L operator*() const { 
        return this->_curr->object();
    }
    Iterator & operator++() { // pre-inc
        this->_curr = this->_curr->next();
        return *this;
    }
    Iterator operator++(int) { // post-inc
        Iterator old = *this;
        this->operator++();
        return old;
    }
    bool operator!=(const Iterator& i) {
        return !(*this == i);
    }
    bool operator==(const Iterator& i) {
        return this->_curr == i._curr;
    }
};

What I needed in this class, respectfully, was: a constructor that allows me return a Node coming from my Linked Lists’s begin(); then overloaders for the iteration, comparisons, and casting. Nest this class inside of the LinkedList class.

Simple and it did the job. What I needed was an iterator class that handles the iterative requirements for the range-based for loop. I also need to provide two accessor methods in my LinkedList class so the for loop can use it. You can see a demonstration of using my LinkedList class here.