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POWhy is Func<> created from Expression<Func<>> slower than Func<> declared directly?
 

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  1. POWhy is Func<> created from Expression<Func<>> slower than Func<> declared directly?
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    <p>Why is a <code>Func&lt;&gt;</code> created from an <code>Expression&lt;Func&lt;&gt;&gt;</code> via .Compile() considerably slower than just using a <code>Func&lt;&gt;</code> declared directly ?</p> <p>I just changed from using a <code>Func&lt;IInterface, object&gt;</code> declared directly to one created from an <code>Expression&lt;Func&lt;IInterface, object&gt;&gt;</code> in an app i am working on and i noticed that the performance went down.</p> <p>I have just done a little test, and the <code>Func&lt;&gt;</code> created from an Expression takes "almost" double the time of an <code>Func&lt;&gt;</code> declared directly.</p> <p>On my machine the Direct <code>Func&lt;&gt;</code> takes about 7.5 seconds and the <code>Expression&lt;Func&lt;&gt;&gt;</code> takes about 12.6 seconds.</p> <p>Here is the test code I used (running Net 4.0)</p> <pre><code>// Direct Func&lt;int, Foo&gt; test1 = x =&gt; new Foo(x * 2); int counter1 = 0; Stopwatch s1 = new Stopwatch(); s1.Start(); for (int i = 0; i &lt; 300000000; i++) { counter1 += test1(i).Value; } s1.Stop(); var result1 = s1.Elapsed; // Expression . Compile() Expression&lt;Func&lt;int, Foo&gt;&gt; expression = x =&gt; new Foo(x * 2); Func&lt;int, Foo&gt; test2 = expression.Compile(); int counter2 = 0; Stopwatch s2 = new Stopwatch(); s2.Start(); for (int i = 0; i &lt; 300000000; i++) { counter2 += test2(i).Value; } s2.Stop(); var result2 = s2.Elapsed; public class Foo { public Foo(int i) { Value = i; } public int Value { get; set; } } </code></pre> <h2>How can i get the performance back ?</h2> <p>Is there anything i can do to get the <code>Func&lt;&gt;</code> created from the <code>Expression&lt;Func&lt;&gt;&gt;</code> to perform like one declared directly ?</p>
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    1. USMartinF
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    1. COInteresting question; I actually get closer to 4x the performance for the direct case.
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      1. USMarc Gravell
    2. CO(my timing is in release, at command line, with full GC before both tests)
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    3. COThere doesnt seem to be a difference if the Func is a Func<int, int>
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