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Why are .NET 4 classes not covariant?

Possible duplicate:
Why isn & rsquo; t there is a common variance for classes in c # 4.0?

As a novice programmer, I have a couple of questions about deviations in .NET 4. Not much about how this works, but why some things are not options, and if other people find it useful.

Question 1:

I know that interfaces and delegates can be covariant / contravariant in .NET 4, but why not classes? So question 1:

List(of BaseClass) = List(of DerivedClass)

Is this something unsafe? Wouldn't that be helpful?

Question 2:

Question 2 follows from question 1, but may be more important for signatures than variances. Suppose I have a MustInherit class with a MustOverride member:

Public MustInherit Class TestBase
    Public MustOverride Property SomeClass as BaseClass
End Class

, SomeClass BaseClass? ? , ?

Public Class TestSpecific
    Inherits TestBase
    Public Overrides Property SomeClass as DerivedClass
End Class

, .NET 4, .

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, #, VB.NET - , . , CLR, .

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+4

Source: https://habr.com/ru/post/1747378/

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