From Java to R OOP
On Mon, Mar 25, 2013 at 6:51 AM, Francisco J. Bido <bido at mac.com> wrote:
Hi, I'm new to OOP in R so please forgive the naiveness of some of the questions. Here are a couple of them. It would be great if you can contrast to OOP in Java.
Java is not the end-all of OOP (in fact S is a good bit older than Java) and you might find that the Lisp or Dylan object systems are a better analogy. (I'm only going by hearsay on Dylan; never used it myself) You might also quickly breeze through: https://github.com/hadley/devtools/wiki/S3
1. R's S4 appears to centered around a dispatch mechanism which in my understanding is just a way to implement polymorphism. Now, here's the snag, I thought polymorphism was an aspect of OOP not by itself the definition of OOP. What am I missing here? Is any language that implements polymorphism automatically OO?
If you accept the immutability of objects, then arguably yes, I suppose polymorphism gives you a great deal of it. The remaining weaknesses are generally addressed by the S4 object system. (Not immutability of bindings like Haskell, but the fact that x <- y <- 1:5; y[3] <- 10 won't change x. In theory this is done by creating a new y with the modified 3rd element and binding the name y to that; not entirely thus in practice for performance reasons )
2. Can someone provide a simple example of how NextMethod() works? I read some things about but I can't make any sense out of it. It's supposed to facilitate inheritance but how? Why is it needed, what happens if it's ignored? An example would be useful. Is there a Java equivalent of NextMethod()?
Grepping through R's source, it seems that the print system uses a fair amount of NextMethod for the AsIs and noquote print methods. You might take a look at those: also, section 7 of http://cran.r-project.org/doc/manuals/r-devel/R-exts.html MW
Many Thanks!
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