I'm curious about why no one has answered my question below. I can't imagine it would be because no one knows how to answer, it must be something basic I am ignorant about. But I have never seen such a pattern, it seems strange to me that a class with an empty definition is automatically virtual, but a class extending it without adding anything is not. I am really puzzled, there must be some design decision behind this, but I can't figure out it's purpose and usefulness. I'd really appreciate an explanation. Thank you. -- Hun Dear R-ers, I don't understand the following, maybe someone will help me explain:
setClasss('A')
[1] "A"
new('a')
Error in new("a") :
trying to generate an object from a virtual class ("a")
setClass('b', contains='a')
[1] "b"
new('b')
An object of class ?b? <S4 Type Object> In what way is B more concrete than A so that it's possible do instantiate B but not A? I don't quite get it. B adds nothing to nothing, and yet it's instantiable, while it's base is not. Makes no sense to me. -- Hun