c#4.0: int a real subtype of object? covariance, ienumerable and value types

Answer 1

Value types aren't LSP-subtypes of object until they're boxed.

Variance doesn't work with value types. At all.

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Demonstration that int is not a proper subtype (subtype in the LSP sense) of object:

Works:

object x = new object();
lock (x) { ... }

Does not work (substitutability violated):

int y = new int();
lock (y) { ... }

Returns true:

object x = new object();
object a = x;
object b = x;
return ReferenceEquals(a, b);

Returns false (substitutability violated):

int y = new int();
object a = y;
object b = y;
return ReferenceEquals(a, b);

Of course, the topic of the question (interface variance) is a third demonstration.