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POLambda Scope Clarification
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  1. POLambda Scope Clarification
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    copied!<p>Why does my parameter <code>x</code> behave so erratically?</p> <ol> <li>Example 1 - Doesn't exist in the current context.</li> <li>Example 2 - Cannot reuse <code>x</code> because it's defined in a 'child' scope.</li> <li>Example 3 - Fine. This is the part where I am confused. Perhaps a different 'child' scope?</li> </ol> <p><strong>Example 1</strong>:</p> <pre><code>List&lt;int&gt; list = new List&lt;int&gt; { 1, 2, 3, 4, 5 }; var result = list.Where(x =&gt; x &lt; 3); Console.Write(result.ElementAt(x)); </code></pre> <p>creates this compile time error:</p> <blockquote> <p>The name 'x' does not exist in the current context</p> </blockquote> <p>which I expect.</p> <p><strong>Example 2</strong>:</p> <pre><code>List&lt;int&gt; list = new List&lt;int&gt; { 1, 2, 3, 4, 5 }; var result = list.Where(x =&gt; x &lt; 3); int x = 1; Console.Write(result.ElementAt(x)); </code></pre> <p>produces this compile-time error:</p> <blockquote> <p>A local variable named 'x' cannot be declared in this scope because it would give a different meaning to 'x', which is already used in a 'child' scope to denote something else</p> </blockquote> <p>I understand the scoping as answered in this question, <a href="https://stackoverflow.com/questions/8898925/is-there-a-reason-for-cs-reuse-of-the-variable-in-a-foreach">Is there a reason for C#&#39;s reuse of the variable in a foreach?</a>. However, this is something I've never seen before. In addition, it makes the answers to this question, <a href="https://stackoverflow.com/questions/10494074/what-is-the-scope-of-a-lambda-variable-in-c">What is the scope of a lambda variable in C#?</a>, incomplete or wrong.</p> <p><strong>Example 3</strong>:</p> <pre><code>List&lt;int&gt; list = new List&lt;int&gt; { 1, 2, 3, 4, 5 }; List&lt;string&gt; stringList = new List&lt;string&gt; { "A", "B" }; var result = list.Where(x =&gt; x &lt; 3); var result2 = stringList.Where(x =&gt; x != "A"); Console.Write(result2); </code></pre> <p>No errors produced.</p> <p><hr /> With the accepted answer, these blog posts from Eric Lippert helped me wrap my head around what was happening. If anyone is still confused:</p> <p><a href="http://blogs.msdn.com/b/ericlippert/archive/2009/08/03/what-s-the-difference-part-two-scope-vs-declaration-space-vs-lifetime.aspx" rel="nofollow noreferrer"><strong>declaration space</strong></a></p> <p><a href="http://blogs.msdn.com/b/ericlippert/archive/2009/11/02/simple-names-are-not-so-simple.aspx" rel="nofollow noreferrer"><strong>simple names</strong></a></p>
 

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