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POWhy is this error "local variable cannot be declared in this scope because it ... is already used"?
 

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  1. POWhy is this error "local variable cannot be declared in this scope because it ... is already used"?
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    <p>I am trying to run the code from the blog article by <a href="http://blogs.msdn.com/b/ericlippert/archive/2006/08/18/why-does-a-recursive-lambda-cause-a-definite-assignment-error.aspx" rel="nofollow">Eric Lippert "Why does a recursive lambda cause a definite assignment error?"</a> </p> <p>but instead of running (or giving the compilation "definite assignment error" I am getting: </p> <blockquote> <p>A local variable named 't' cannot be declared in this scope because it would give a different meaning to 't', which is already used in a 'parent or current' scope to denote something else </p> </blockquote> <p>Why?<br> Where is it already used in parent or current scope?<br> Tried to rename it having gotten the same error<br> How should I change the code to launch this code? </p> <pre><code>using System; namespace LippertRecursiveLambdaError { class Program { static void Main(string[] args) { Tree&lt;int&gt; tree = new Tree&lt;int&gt; (3, new Tree&lt;int&gt; (4, new Tree&lt;int&gt;(1), null), new Tree&lt;int&gt;(5)); PrintTree(tree); Console.ReadLine(); } delegate void Action&lt;A&gt;(A a); delegate void Traversal&lt;T&gt;(Tree&lt;T&gt; t, Action&lt;T&gt; a); static void DepthFirstTraversal&lt;T&gt;(Tree&lt;T&gt; t, Action&lt;T&gt; a) { if (t == null) return; a(t.Value); DepthFirstTraversal(t.Left, a); DepthFirstTraversal(t.Right, a); } static void Traverse&lt;T&gt;(Tree&lt;T&gt; t, Traversal&lt;T&gt; f, Action&lt;T&gt; a) { f(t, a); } static void Print&lt;T&gt;(T t) { System.Console.WriteLine(t.ToString()); } /*static void PrintTree&lt;T&gt;(Tree&lt;T&gt; t) { Traverse(t, DepthFirstTraversal, Print); }*/ static void PrintTree&lt;T&gt;(Tree&lt;T&gt; t) { //Traversal&lt;T&gt; df = (t, a)=&gt; ************** Traversal&lt;T&gt; df = null; //======================================== //The next line gives compilation error //A local variable named 't' cannot be declared in this scope //because it would give a different meaning to 't', //which is already used in a 'parent or current' scope to denote something else df = (t, a) =&gt; { if (t == null) return; a(t.Value); df(t.Left, a); df(t.Right, a); }; Traverse(t, df, Print); }//PrintTree }//class class Tree&lt;T&gt; { public Tree&lt;T&gt; Left; public Tree&lt;T&gt; Right; public T Value; public Tree(T value) { Value = value; } public Tree(T value, Tree&lt;T&gt; left, Tree&lt;T&gt; right) { Value = value; Left = left; Right = right; } } }//namespace </code></pre>
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    1. USecatmur
    1. USFulproof
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      1. POWhy is this error "local variable cannot be declared in this scope because it ... is already used"?
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      1. VTUpMod
    1. COI assume this is C#, not C (or C++, or Java).
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      1. POWhy is this error "local variable cannot be declared in this scope because it ... is already used"?
      1. USecatmur
    2. CO@ecatmur It is definitely C#
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      1. POWhy is this error "local variable cannot be declared in this scope because it ... is already used"?
      1. USLews Therin
    3. COIt is C#. I don't know why/how java skipped into tags. My error
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      1. POWhy is this error "local variable cannot be declared in this scope because it ... is already used"?
      1. USFulproof
 

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