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POC++ std::iterator without using std::vector or std::list internally
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  1. POC++ std::iterator without using std::vector or std::list internally
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    copied!<p>I'm trying (as an exercise) to create a simple numeric range class in C++. It will let you iterate through evenly spaced doubles (like the numpy/Python <code>arange</code>):</p> <p><strong>What I'd like to do (but with an iterator):</strong></p> <pre><code>double lower = ..., upper = ..., delta = ...; for (double val = lower; val &lt; upper; val += delta) { // do something with val f(val); } // include the last val to guarantee upper is included or exceeded f(val); // do something with val </code></pre> <p><strong>Desired equivalent iterator code:</strong> </p> <pre><code>double lower = ..., upper = ..., delta = ...; NumericRange nr(lower, upper, delta); for (NumericRange::const_iterator iter = nr.begin(); iter != nr.end(); iter++) { f(*iter); } </code></pre> <p>I'd like my iterator to be compatible with STL iterators so I can reuse code (iterating through a NumericRange should be equivalent to iterating through std::vector).</p> <p>I've had success simply storing the values in a std::vector (and then using the std::vector's iterator). This is how everything I've found online has solved this problem. However, it really isn't necessary to store the entire list.</p> <p><strong>Is there a way to avoid storing the entire set of values? Is there some <code>iterable</code> class I can inherit from and override <code>++</code>, <code>==</code>, etc. to get the desired effect without storing the <code>std::vector&lt;double&gt;</code>?</strong> <br></p> <p>(I'd really like to know how to do this without BOOST, even though it's great. I'm asking this because I'd like to learn how to <em>write</em> (from scratch) something like a BOOST solution. I definitely know that part of software engineering is using the tools created by others, but I really want to learn how those tools are designed and built.)</p> <p><strong>My iterable NumericRange class (using <code>std::vector&lt;double&gt;</code> internally):</strong></p> <pre><code>class NumericRange { protected: double lower, upper, delta; std::vector&lt;double&gt; sorted_range; public: typedef std::vector&lt;double&gt;::const_iterator const_iterator; NumericRange() { lower = upper = delta = std::numeric_limits&lt;double&gt;::quiet_NaN(); // vector is constructed empty } NumericRange(double lower_param, double upper_param, double delta_param) { lower = lower_param; upper = upper_param; delta = delta_param; assert(upper_param &gt; lower_param); double val; // note: can be much faster without push_back for (val = lower_param; val &lt; upper_param; val += delta_param) { sorted_range.push_back(val); } // ensure the upper_value is contained or surpassed sorted_range.push_back(val); } // to prevent comparison of the entire vector bool operator ==(const NumericRange &amp; rhs) const { return lower == rhs.lower &amp;&amp; upper == rhs.upper &amp;&amp; delta == rhs.delta; } // note: this class doesn't really need to store the values in a // vector, but it makes the iterator interface much easier. const_iterator begin() const { return sorted_range.begin(); } const_iterator end() const { return sorted_range.end(); } double get_lower() const { return lower; } double get_upper() const { return upper; } double get_delta() const { return delta; } size_t size() const { return sorted_range.size(); } void print() const { std::cout &lt;&lt; "[ " &lt;&lt; lower &lt;&lt; " : " &lt;&lt; upper &lt;&lt; ": +=" &lt;&lt; delta &lt;&lt; " ]" &lt;&lt; std::endl; } }; </code></pre>
 

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