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POWhy are .NET value types sealed?
 

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    <p>It's not possible to inherit from a C# struct. It's not obvious to me why this is:</p> <ul> <li>Clearly you can't have a reference type that inherits from a value type; this wouldn't work</li> <li>It doesn't sound reasonable to inherit from one the primitive types (Int32, Double, Char, etc.)</li> <li>You'd need to be able to call (non-virtual) methods on the base using a derived instance. You could cast from a derived struct to the base, since they would overlap the same memory. I guess casting from a base to derived wouldn't work, since you couldn't know the type of the derived struct at runtime.</li> <li>I can see that you couldn't implement virtual methods in your class hierarchy, since value types can't have virtual members</li> </ul> <p>I wonder if this is a technical limitation in the CLR, or something that the C# compiler stops you from doing?</p> <p><strong>Edit:</strong> Value types can't have virtual methods, and I realise this limitation rules out most scenarios in which you'd want to use inheritance. That still leaves inheritance-as-aggregation, though. Imagine a <code>Shape</code> struct with a <code>Colour</code> field: I can write code that accepts any struct derived from <code>Shape</code>, and access its <code>Colour</code> field, even if I can never write a virtual <code>Shape.Draw</code> method.</p> <p>I can think of one scenario that would get broken by non-sealed value types. Value types are supposed to implement <code>Equals</code> and <code>GetHashCode</code> correctly; even though these two methods on <code>System.Object</code> are virtual, they get called non-virtually on value types. Even if value types weren't sealed, someone writing a struct derived from another one couldn't write their own implementation of these two methods and expect to have them called correctly.</p> <p>I should point out that I'm not suggesting I should be able to inherit from structs in my own code. What I am trying to do, though, is to guess why this particular code smell is forbidden by .NET.</p> <p><strong>Edit 2:</strong> I just spotted <a href="https://stackoverflow.com/questions/1222935/why-dont-structs-support-inheritance">this very similar question</a>, the answer to which is effectively "because then arrays of value types wouldn't work".</p>
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    1. COpossible duplicate of [Why don't structs support inheritance?](http://stackoverflow.com/questions/1222935/why-dont-structs-support-inheritance)
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