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POC# design: Why is new/override required on abstract methods but not on virtual methods?
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copied!<p>Why is new/override required on abstract methods but not on virtual methods?</p> <p>Sample 1:</p> <pre><code>abstract class ShapesClass { abstract public int Area(); // abstract! } class Square : ShapesClass { int x, y; public int Area() // Error: missing 'override' or 'new' { return x * y; } } </code></pre> <p>The compiler will show this error: <em>To make the current member override that implementation, add the override keyword. Otherwise add the new keyword</em></p> <p>Sample 2:</p> <pre><code>class ShapesClass { virtual public int Area() { return 0; } // it is virtual now! } class Square : ShapesClass { int x, y; public int Area() // no explicit 'override' or 'new' required { return x * y; } } </code></pre> <p>This will compile fine, by hiding the method by default.</p> <p>I fully understand the technical differences. However I wonder why the language was designed that way. Wouldn't it be better to have the same restriction in "Sample 2" as well? I mean in most cases if you create a method with the same name as in the parent class, you usually intent to override it. So I think explicitly stating Override/New would make sense on virtual methods as well.</p> <p>Is there a design-wise reason for this behavior?</p> <p><strong>Update:</strong> The 2nd sample actually causes a warning. The first sample shows an error because the subclass is required to implement the abstract method. I didn't see the warning in VS.. makes perfectly sense to me now. Thanks.</p>

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