Re: Mixing self conscious parametrized types with inheritance

Lew <>
Tue, 15 Mar 2011 11:21:16 -0700 (PDT)
On Mar 15, 9:54 am, SoulSpirit <> wrote:

On Tuesday, March 15, 2011 2:16:13 PM UTC+1, Robert Klemme wrote:


Why do you insist that only Comparable<ConcreteType> is
valid and not Comparable<TypyParameter>?

Because if the type implements 'compareTo()' for some other type, it's
making an incorrect type assertion. It's saying, in your case, that
'BaseC' implements comparison for 'SC', not for itself.

I agree with you, Robert.
Just look at the standard java Enum class. It is declared as:

public abstract class Enum<E extends Enum<E>>
  implements Comparable<E>, Serializable

That's different. You aren't implementing 'compareTo()' for 'Enum'
itself. 'Enum' has no implementation of 'compareTo()', so there's no
method with which the subtypes can conflict, unlike Robert's example.

Robert is trying to implement the *base type* compareTo() in terms of
subtypes, that's the problem. 'Enum' doesn't make that mistake.

Apples and oranges.


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