Why cannot derive from value types in C#?

Question

I know that all value types are derived implicitly from the System.ValueType. and structs can implement interfaces, but I need to know why cannot derive from value types in C#.

Answer 1

Firstly, value-types have no object header (because they aren't objects), so there would be no way to identify the actual type, or to do virtual dispatch.

Secondly - how could you add fields to sub types? The size has to be known by the compiler (for stack space etc), so:

Foo foo = ...

must always take the same amount of space.

Likewise, an abstract base-type wouldn't work, as you can always construct a struct.

Basically, they would be horrible malformed things, crippled and ugly.

I find it interesting that you would want a subtype of a value - that sounds a bit like a confused usage of a struct.