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    <p>Most .Net languages including C# and VB do not use the tail recursion feature of MSIL code.</p> <p>Tail recursion is an optimization that is common in functional languages. It occurs when a method A ends by returning the value of method B such that method A's stack can be deallocated once the call to method B is made.</p> <p>MSIL code supports tail recursion explicitly, and for some algorithms this could be a important optimization to make. But since C# and VB do not generate the instructions to do this, it must be done manually (or using F# or some other language).</p> <p>Here is an example of how tail-recursion may be implemented manually in C#:</p> <pre><code>private static int RecursiveMethod(int myParameter) { // Body of recursive method if (BaseCase(details)) return result; // ... return RecursiveMethod(modifiedParameter); } // Is transformed into: private static int RecursiveMethod(int myParameter) { while (true) { // Body of recursive method if (BaseCase(details)) return result; // ... myParameter = modifiedParameter; } } </code></pre> <p>It is common practice to remove recursion by moving the local data from the hardware stack onto a heap-allocated stack data structure. In the tail-call recursion elimination as shown above, the stack is eliminated completely, which is a pretty good optimization. Also, the return value does not have to walk up a long call-chain, but it is returned directly.</p> <p>But, anyway, the CIL provides this feature as part of the language, but with C# or VB it has to be implemented manually. (The jitter is also free to make this optimization on its own, but that is a whole other issue.)</p>
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    1. POWhat can you do in MSIL that you cannot do in C# or VB.NET?
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    1. USJeffrey L Whitledge
    1. USJeffrey L Whitledge
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    1. COF# does not use MSIL's tail recursion, because it only works in fully trusted (CAS) cases because of the way it does not leave a stack to check for permission assrtions (etc.).
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      1. USRichard
    2. CORichard, I'm not sure what you mean. F# certainly does emit the tail. call prefix, pretty much all over the place. Examine the IL for this: "let print x = print_any x".
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      1. USMichaelGG
    3. COI believe that the JIT will use tail recursion anyway in some cases - and in some cases will ignore the explicit request for it. It depends on the processor architecture, IIRC.
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      1. USJon Skeet
 

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