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    <blockquote> <p>Is there some iterable 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>? </p> </blockquote> <p>Yes, there is. Its name is <code>std::iterator&lt;std::input_iterator_tag, double&gt;</code>.</p> <p>Here is a start for you, using <code>int</code>. To save space in my brain, I use the same class to represent both the range and the iterator.</p> <pre><code>#include &lt;iterator&gt; #include &lt;iostream&gt; struct NumericRange : public std::iterator&lt; std::input_iterator_tag, int &gt; { int current, fini, delta; typedef NumericRange iterator; typedef iterator const_iterator; iterator begin() { return *this; } iterator end() { return iterator(fini, fini, delta); } iterator&amp; operator++() { current += delta; return *this; } iterator operator++(int) { iterator result(*this); ++*this; return result; } int operator*() const { return current; } NumericRange(int start, int fini, int delta) : current(start), fini(fini), delta(delta) { } bool operator==(const iterator&amp; rhs) { return rhs.current == current; } bool operator!=(const iterator&amp; rhs) { return !(*this == rhs); } }; void f(int i, int j) { std::cout &lt;&lt; i &lt;&lt; " " &lt;&lt; j &lt;&lt; "\n"; } int main () { int lower = 4, upper = 14, delta = 5; NumericRange nr(lower, upper, delta); for (NumericRange::const_iterator iter = nr.begin(); iter != nr.end(); iter++) { f(*iter, *nr.end()); } } </code></pre>
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    1. POC++ std::iterator without using std::vector or std::list internally
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    1. COAwesome, thanks a lot. It's a bit more difficult with `double` because the `!=` operator compares `double`s for direct equality, which is numerically dangerous. To do so, you must guarantee that successively performing `current += delta` will eventually result in `current == fini`; this is not necessarily the same as `fini = current + k*(delta)` where k is an integer, because of numerical error. For this reason, I would bound the numerical error and test for approximate equality within this bound when doing `!=`.
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    2. COYep, that's why I started with `int`. Making a version for double is left as an exercise.
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