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POHow to copy iterator in Scala?
 

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  1. POHow to copy iterator in Scala?
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    <h2>About duplicate</h2> <p><em>This is NOT a duplicate of <a href="https://stackoverflow.com/questions/5220108/a-very-simple-question-how-to-clone-an-iterator">How to clone an iterator?</a></em></p> <p>Please do not blindly close this question, all the answers given in so-called duplicate <strong>DO NOT</strong> work. The OP is in charge of the other problem, and obviously, the answers fitted HIS problem, but not mine.</p> <p>Not every similar question is a duplicate, there is such feature as "expansion question" on SE, the only way is to ask again on the same subject to get different, working, answers.</p> <h2>Problem</h2> <p>I have iterator. I would like to get copy (duplicate) of it, so then I could proceed with original and copy completely independently.</p> <p><strong>Important</strong></p> <p>Copying through reflection or serialization is no-go (performance penalty).</p> <p><strong>Example</strong></p> <pre><code>var list = List(1,2,3,4,5) var it1 = list.iterator it1.next() var it2 = it1 // (*) it2.next() println(it1.next()) </code></pre> <p>This would make simply reference to <strong>it1</strong>, so when changing <strong>it1</strong>, <strong>it2</strong> changes as well and vice-versa.</p> <p><em>The example above uses <strong>List</strong>, I am currently struggling with <strong>HashMap</strong>, but the question is general one -- just iterator.</em></p> <h3>Approach #1</h3> <p>If you edit line (*) and write:</p> <pre><code>var it2 = it1.toList.iterator </code></pre> <p>(this was suggested as solution in the linked question) the exception is thrown while executing the program.</p> <h3>Approach #2</h3> <p>"You take the list and...". No, I don't. I don't have a list, I have iterator. In general I don't know anything about collection which underlies the iterator, the only thing I have is iterator. I have to "fork" it.</p>
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    1. COThis is a duplicate. Use my answer for the other question; it works in all cases. (The method is also called `duplicate`.)
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    2. COI have edited Miles' answer on the other page to highlight that what you tried to do here will not work and give a working solution.
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    3. CO@Rex Kerr, no, it is not duplicate judging by answers. The answers given in the other question answers the OTHER question and they DO NOT fit my question. I appreciate your answers, they are educational and for sure I know more, but they don't solve THIS problem.
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