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POOptimally and elegantly performing certain behaviors based on types in a hierarchy
 

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  1. POOptimally and elegantly performing certain behaviors based on types in a hierarchy
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    <p>I am trying to optimize a certain part of my code, which happens to be in a tight performance loop. Mainly I am trying to learn new things which I can apply in the future. My implementation is very lengthy, so I will give a general example of what I am trying to achieve. </p> <p>My question relates to this: <a href="https://stackoverflow.com/questions/686412/c-sharp-is-operator-performance">C# &#39;is&#39; operator performance</a>, and especially to the chosen answer.</p> <p>Say I have a class A. I also have a class B, which is derived from A. I have a list of type A (which contains a mix of A and B types). In a method where I process these items, I would like to achieve a certain behaviour based on the actual type of the object (not sure if this is the correct way of saying it. Please correct me wherever I say something wrong).</p> <pre><code>void Process(A item) { if (item is A) { DoBehavior((A)item); //I know the cast is redundant here, I'm just leaving //it here for my explanation. } else if (item is B) { DoBehavior((B)item); } } void DoBehaviour(A item) { //perform necessary behaviour for type A } void DoBehaviour(B item) { //perform necessary behaviour for type B } </code></pre> <p>This is the way I currently do it. Note that I iterate over a list of type A, which contains A's and B's. Also, if you feel I did not provide enough code to clarify the situation, I'll gladly expand.</p> <p>In the question I posted above: <a href="https://stackoverflow.com/questions/686412/c-sharp-is-operator-performance">C# &#39;is&#39; operator performance</a>, I have learnt that I can rather change the structure to use an "as" operator, and completely get rid of the explicit cast.</p> <pre><code>B bItem = item as B; if (bItem != null) { DoBehavior(bItem); } </code></pre> <p>This is all good, however, in actuality I do not just have an A and a B, I also have a C, a D, and so on, all deriving from base class A. This will lead to many of these if statements, and they would have to be nested for best performance:</p> <pre><code>B bItem = item as B; if (bItem != null) { DoBehavior(bItem); } else { C cItem = item as C; if (cItem != null) { DoBehavior(cItem); } else { //and so on. } } </code></pre> <p>Now this is ugly. I like writing neat, elegant code, yet I am exceptionally bad at doing it (which often leads me to wasting time trying to just make things look a little better).</p> <p>I hope this question is not to broad, but firstly I would like to know if there is a more optimal and clean solution at getting the type so that the relevant behavior is performed. If not, is there a cleaner way to use these 'as' operators than nesting it like this?</p> <p>I suppose one alternative would be to move the behavior into the base class A, and then overriding it for each derived class. However, in a higher thinking sense, the behavior in this particular case of mine is not a behavior of the class A (or it's children), rather, it is some external class acting/behaving on it (which will behave differently for each type). If there is no better way to do it, I will strongly consider implementing it as I have explained now - but I would like some expert opinions on this.</p> <p>I tried to keep this short, and may have left too much detail out. Let me know if this is the case.</p>
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    1. COThis looks like a good place to implement the visitor pattern.
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      1. USKelly Ethridge
    2. COThat first cast isn't redundant at all!
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    3. COI just learnt about the visitor pattern 5 minutes ago, from a related question I had.
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