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POIs there a good reason why extension method classes can't be nested?
 

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  1. POIs there a good reason why extension method classes can't be nested?
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    <p>I've been using extension methods a lot recently to help make my code be more fluent, but I keep running into situations where I can't limit the exposure of the functionality I've created in the way I'd like.</p> <p>Say I have some code like this (completely made up example):</p> <pre><code>var liveSet = allitems.Where(x =&gt; x.Status == Status.Live).Select(x =&gt; x.Name); var deadSet = allitems.Where(x =&gt; x.Status == Status.Dead).Select(x =&gt; x.Name); var zombieSet = allitems.Where(x =&gt; x.Status == Status.Neither).Select(x =&gt; x.Name); </code></pre> <p>I'd like to make this more fluent, and stop repeating myself:</p> <pre><code>var liveSet = allitems.SelectNameWhere(x =&gt; x.Status == Status.Live); ... </code></pre> <p>But I consider this to be a helper method, not a true extension and so I would like to limit its usage in the same way as I can a private method:</p> <pre><code>//In the same class private static IEnumerable&lt;string&gt; SelectNameWhere( this IEnumerable&lt;Element&gt; items, Func&lt;Element, bool&gt; predicate) ... </code></pre> <p>Unfortunately I can't do this because the class that holds the extension method must be static. Okay, not the end of the world, I'll nest a private static class to hold the method... Of course I can't do that either, so I'm left either exposing this method to at least an internal level, or removing the nice, fluent, nature of my code:</p> <pre><code>var liveSet = SelectNameFrom(allItems, x =&gt; x.Status == Status.Live); ... </code></pre> <p>These limitations on where you can declare an extension method seem fairly arbitrary to me, but I assume they have good logical or technical reasons. If so, what are they? </p>
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    1. USMartin Harris
    1. USMartin Harris
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    1. COCan't comment on the technicalities of the question as I don't know the answer. But it looks like you're trying to shoehorn functionality into extension methods that doesn't really belong there. Implement these examples through a repository, and your problem goes away. Extensions are *supposed* to be global. A need to lock down their access is a pretty bad code smell imho.
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      1. USfearofawhackplanet
    2. COI agree that it would often be useful to declare "local" extension methods in a nested class. Alternatively, you can declare them in a separate namespace, so they don't show up everywhere
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      1. USThomas Levesque
    3. COI agree that there should be a way to limit the scope of the extension method based on class (not just namespace).
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