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POHow do you implement type-specific functionality when using polymorphism does NOT make sense?
 

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  1. POHow do you implement type-specific functionality when using polymorphism does NOT make sense?
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    <p>A common red flag that an OOP language is not being leveraged properly looks like this:</p> <pre><code>if (typeof(x) == T1) { DoSomethingWithT1(x); } else if (typeof(x) == T2) { DoSomethingWithT2(x); } </code></pre> <p>The standard "fix" for such design issues is to make <code>T1</code> and <code>T2</code> both share an interface, either through inheritance of a base type or implementation of a common interface (in languages that support it); for example, in C# a solution might be:</p> <pre><code>public interface IT { void DoSomething(); } </code></pre> <p>However, sometimes you want to implement functionality that differs based on the type of an object but that functionality does <em>not</em> belong within that object's type; thus polymorphism seems the wrong way to go.</p> <p>For example, consider the case of a UI that provides a view of a given clump of data. Supposing this view is capable of rendering various layouts and controls depending on the type of data being presented, how would you implement this type-specific rendering without a bunch of <code>if</code>/<code>else</code> statements?</p> <p>For reasons that I <em>hope</em> are obvious, putting the rendering logic in the type itself strikes me as a very bad decision in this case. On the other hand, without coupling the type of data object to its visual presentation I have a hard time seeing how the <code>if</code>/<code>else</code> scenario is avoided.</p> <p>Here's a concrete example: I work on a trading application which utilizes many different pricing models for various market products. These different models are represented by types inheriting from a common <code>PricingModel</code> base; and each type is associated with a completely different set of parameters. When the user wants to view the parameters for a particular pricing model (for a particular product), currently these are displayed by a form which detects the type of the model and displays an appropriate set of controls. My question is how this could be implemented more elegantly than it is currently (with a big <code>if</code>/<code>else</code> block).</p> <p>I realize this probably seems like a very basic question; it's just one of those gaps in my knowledge (of solid OOP principles? design patterns? common sense?) that I figured it's about time to fix.</p>
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