> The class AB inherits from A and from B, but B already inherits from class A.
> So actually you only have an object of class B in your object of class AB.
> When you call the function f R looks for a method f for AB objects. It does
> not find such a method and looks for a method of the object inherited from,
> B. Such a method is present and is then executed.
>
> The inheritance structure has to be changed. The behavior is actually
> desired, as if this behavior weren't given a diamond class inheritance would
> be fatal.
Are you sure? That behaviour doesn't agree with the description of
method dispatch given in ?Methods, not with getClass("AB") which shows
that AB inherits from both A and B. (I totally agree that this is a
bad idea, and unlikely to be useful in real life, but I'm trying to
understand the details of S4 dispatch)
> getClass("AB")
Class "AB" [in ".GlobalEnv"]
Slots:
Name: .xData
Class: NULL
Extends:
Class "B", directly
Class "A", directly
Class ".NULL", by class "A", distance 2
Class "NULL", by class "A", distance 3, with explicit coerce
Class "OptionalFunction", by class "A", distance 4, with explicit coerce
Class "optionalMethod", by class "A", distance 4, with explicit coerce
--
Chief Scientist, RStudio
http://had.co.nz/
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