Why can't I write Nullable>?

Question

The definition of Nullable is:

[SerializableAttribute]
public struct Nullable where T : struct, new()

The constraint

Answer 1

This isn't exactly an answer, but just food for thought.

Round 1

Nullable> a;

error CS0453: The type 'int?' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'Nullable'

Intellisense hints... The name can be simplified

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Round 2

Nullable a;

error CS0453: The type 'int?' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'Nullable'

Intellisense hints... The name can be simplified

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Round 3

int?? a;

error CS1519: Invalid token '??' in class, struct, or interface member declaration

error CS1525: Invalid expression term '??'

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Conclusion

int? is essentially just a short-hand evaluation of Nullable, but there's no such thing as int?? which is the only way I can see of representing Nullable> in short-hand. Plus int?? borrows the null-coalescing operator, so I'm glad it's not possible because it looks dreadful. Imagine int????????????? a; How pointless.

Finally, since the reference source for Nullable does not yield any constraints for enforcing this, my guess is that this constraint was baked into the CLR as a special case when nullable value types were introduced into C#.