Create range from single value

only.cpp

#include <iterator>
#include <string>
#include <cassert>

template<typename T>
struct Only
{
    struct iterator : public std::iterator<std::forward_iterator_tag, T>
    {
        iterator(Only* only, bool isEnd = false) : _only(only), _isEnd(isEnd) {
            
        }
        
        T& operator*() {
            return _only->_value;
        }
        const T& operator*() const {
            return _only->_value;
        }
        T* operator->() {
            return &_only->_value;
        }
        const T* operator->() const {
            return &_only->_value;
        }
        iterator operator++() {
            if (!_isEnd) {
                _isEnd = true;
            }
            return *this;
        }
        iterator operator++(int) {
            iterator toReturn = *this;
            ++(*this);
            return toReturn;
        }
        bool operator==(const iterator& other) const {
            return equal(other);
        }
        bool operator!=(const iterator& other) const {
            return !equal(other);
        }
    private:
        bool equal(const iterator& other) const {
            return (_only == other._only) && ((_isEnd && other._isEnd) || (!_isEnd && !other._isEnd && _only->_value == other._only->_value));
        }
        
        Only* _only;
        bool _isEnd;
    };
    
    Only(const T& value) : _value(value) {
        
    }
    
    iterator begin() {
        return iterator(this);
    }
    iterator end() {
        return iterator(this, true);
    }
    
private:
    T _value;
};

int main (int argc, char** argv) {
    
    Only<std::string> only("Hello");
    assert(only.begin() != only.end());
    
    Only<std::string>::iterator first = only.begin();
    assert(*first == "Hello");
    assert(first->size() == 5);
    
    Only<std::string>::iterator first2 = first++;
    assert(first == only.end());
    assert(first2 == only.begin());
    
    first = ++first2;
    assert(first == first2);
    assert(first2 == only.end());
    
    return 0;
}