/* A python like range for C++ that can be used with range based for loops. A range based for loop requires: a. iterators begin and end b. overloaded prefix increament(++) operator c. overloaded != operator. This is to check when to stop the execution. */ /* Here is my attempt. Let me know the mistakes. Suggestion for improvements are always welcomed :) */ #include template class Range { // forward reference struct Iterator; friend struct Iterator; public: Range( T const &begin, T const &end, T const &step) : m_begin(begin), m_end(end) { // for cases like range(1, 10, 2) // or a range like range(5, -5, -1) if((m_begin < m_end && step > 0) || (m_begin > m_end && step < 0)) { m_step = step; m_end = m_begin + ((m_end - m_begin) / m_step) * m_step; if (end - m_end > 0) m_end += m_step; } /* for cases like range(1, 10, -2) or like range (10,1,1) this is an invalid range hence the process must exit gracefully. So set m_begin and m_end to 0 */ else if((m_begin < m_end && step < 0) || (m_begin > m_end && step> 0)){ m_begin = m_end = 0; } } // end Range constructor // range based for loop requires begin and // end iterator Iterator begin() { return m_begin; } Iterator end() { return m_end; } private: T m_begin; // starting of sequence T m_end; // one past the last value // distance between adjacent values // in the sequence. static T m_step; private: struct Iterator { T m_val; // the actual value Iterator(T const &val):m_val(val) {} // dereference operator for range // based for loop T operator*() const { return m_val; } // end condition for the range-based for // loops bool operator !=(T const &other)const { return m_val != other; } // must provide prefix increament // for range based for loop Iterator & operator++() { m_val += m_step; return *this; } // implicit type conversion operator T() const { return m_val; } }; // end struct Iterator }; // static variable initialization template T Range :: m_step = 1; // Helper methods for creating an object // of class Range that can be used template < typename T > Range < T > range(T const &begin, T const &end, T const &step) { return Range (begin, end, step); } /* Argument asPython=true by default. As a result there is no output for a range like range(5, -5) or range(0, -5) or range(-5, -9) If asPython = false then a range like range(5,-5) prints 5,4,3,2,1,0,-1,-2,-3,-4 or a range like range(-5,-9) prints -5, -6, -7, -8 Note if the range is valid then then asPython=false still produce the right result e.g. range(-5,5, false) will still print -5, -4, -3, -2, -1, 0, 1, 2, 3, 4 */ template Range range(T const &begin, T const &end, bool asPython=true) { T step; if(! asPython) { step = begin < end ? T(1) : -T(1); } else { step = T(1); } return Range (begin, end, step); } /* Argument asPython = true by default as a result there will be no output for a range like range(-5). If asPython = false then a range like range(-5) prints 0, -1, -2, -3, -4 Note if the range is valid then then asPython=false still produce the right result e.g. range(5, false) will still print 0, 1, 2, 3, 4 */ template Range range(T const &arg, bool asPython=true) { // asPython = true then for arg < 0 output // should be zero T step; if(! asPython) { step = arg < 0 ? -T(1) : T(1); } else { step = 1; } return Range (0,arg,step); } auto main()->int { // Test cases // prints: 1, 3, 5, 7, 9 std::cout << "range(1,10,2) = "; for (auto const &x:range(1, 10, 2)) std::cout << x << " "; std::cout << "\n"; // prints: -1, 1, 3, 5 std::cout << "range(-1, 7, 2) = "; for (auto const &x:range(-1, 7, 2)) std::cout << x << " "; std::cout << "\n"; // no output std::cout << "range(-5) = "; for (auto const &x:range(-5)) std::cout << x << " "; std::cout << "\n"; // prints 0, -1, -2, -3, -4 std::cout << "range(-5,false) = "; for (auto const &x:range(-5, false)) std::cout << x << " "; std::cout << "\n"; // prints 0, 1, 2, 3, 4 std::cout << "range(5) = "; for (auto const &x:range(5)) std::cout << x << " "; std::cout << "\n"; // no output std::cout << "range(5,-5) = "; for (auto const &x:range(5,-5)) std::cout << x << " "; std::cout << "\n"; std::cout << "range(5,-5,false) = "; for (auto const &x:range(5,-5, false)) std::cout << x << " "; std::cout << "\n"; std::cout << "range(-5,5) = "; for (auto const &x:range(-5,5)) std::cout << x << " "; std::cout << "\n"; // the last argument is false but rhe range is valid hence output produced is valid as -5, -4, -3, -2, -1, 0, 1, 2, 3, 4 std::cout << "range(-5,5,false) = "; for (auto const &x:range(-5,5,false)) std::cout << x << " "; std::cout << "\n"; std::cout << "range(-5,-9) = "; for (auto const &x:range(-5, -9)) std::cout << x << " "; std::cout << "\n"; std::cout << "range(-5,-9,false) = "; for (auto const &x:range(-5, -9,false)) std::cout << x << " "; std::cout << "\n"; std::cout << "range(0,5) = "; for (auto const &x:range(0, 5)) std::cout << x << " "; std::cout << "\n"; // no output std::cout << "range(5,0) = "; for (auto const &x:range(5, 0)) std::cout << x << " "; std::cout << "\n"; // print 5,4,3,2,1 std::cout << "range(5,0,false) = "; for (auto const &x:range(5, 0,false)) std::cout << x << " "; std::cout << "\n"; for(auto const &x : range(-1, -10, -2)) std::cout << x << " "; std::cout << std::endl << "ending main"; return 0; }

cppRange.cpp