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    <p>Personally I like Mark Byer's option, but you could always write your own generic method for this:</p> <pre><code>public static void IterateWithSpecialFirst&lt;T&gt;(this IEnumerable&lt;T&gt; source, Action&lt;T&gt; firstAction, Action&lt;T&gt; subsequentActions) { using (IEnumerator&lt;T&gt; iterator = source.GetEnumerator()) { if (iterator.MoveNext()) { firstAction(iterator.Current); } while (iterator.MoveNext()) { subsequentActions(iterator.Current); } } } </code></pre> <p>That's relatively straightforward... giving a special <em>last</em> action is slightly harder:</p> <pre><code>public static void IterateWithSpecialLast&lt;T&gt;(this IEnumerable&lt;T&gt; source, Action&lt;T&gt; allButLastAction, Action&lt;T&gt; lastAction) { using (IEnumerator&lt;T&gt; iterator = source.GetEnumerator()) { if (!iterator.MoveNext()) { return; } T previous = iterator.Current; while (iterator.MoveNext()) { allButLastAction(previous); previous = iterator.Current; } lastAction(previous); } } </code></pre> <p>EDIT: As your comment was concerned with the performance of this, I'll reiterate my comment in this answer: while this general problem is reasonably common, it's <em>not</em> common for it to be such a performance bottleneck that it's worth micro-optimizing around. Indeed, I can't remember ever coming across a situation where the looping machinery became a bottleneck. I'm sure it happens, but <em>that</em> isn't "common". If I ever run into it, I'll special-case that particular code, and the best solution will depend on <em>exactly</em> what the code needs to do.</p> <p>In general, however, I value readability and reusability <em>much</em> more than micro-optimization.</p>
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    1. POOther ways to deal with "loop initialization" in C#
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    1. USJon Skeet
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    1. CO+1 for showing the correct way to use an enumerator directly: `using`.
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      1. USR. Martinho Fernandes
    2. COBut calling a delegate is rather expensive action (delegate `Action`) so this solution is meant to be legible but it is on the expense of performance. Am I right or is there a trick?
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      1. USMartin Vseticka
    3. CO@MartyIX: Your question talks about a *common* coding problem, but also specifies performance as a key requirement. Just how often does this crop up in such a way that the cost of executing a delegate is going to be a bottleneck? I can't think of that *ever* happening to me. If I ever ran into it, I'd treat that specific situation as an anomaly, and write code specific to it. I wouldn't try to think of a general purpose solution to such an unusual situation. "General purpose" is often counter to the kind of micro-optimization it looks like you're after.
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