[Rd] Reference Classes: (Was: Accessing methods via [[...]], bug?)

John Chambers jmc at r-project.org
Wed May 4 18:35:24 CEST 2011

On 5/4/11 9:24 AM, Hadley Wickham wrote:
>>> Are you familiar with "Concepts, Techniques, and Models of Computer
>>> Programming" by van Roy and Haridi?  That's what really helped me to
>>> understand the strengths and weaknesses of the various styles of
>>> programming.
>> Thanks, I wasn't.  Yes, interesting similar distinction between functional
>> and "type" decomposition.  An important associated aspect for us is the
>> distinction between reference objects and "ordinary" R objects, not AFAICS
>> conveyed by their more abstract treatment.
> Another discussion I found useful was in SICP:
> http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-17.html#%_sec_2.4.3
> I really like the metaphor of method dispatch as a table with types in
> the columns and operations in the rows - then you can think of generic
> functions oo as being row-based, and class based oo as column-based.

Except that functional method dispatch with multiple dispatch is 
dispatched on a K-tple of classes if the generic function has K 
arguments in its signature.

This is not a trivial distinction because it means that a method can 
depend on more than one class definition, so it's not just a matter of 
distributing the same information in different ways, but a fundamentally 
more complicated structure for functional OOP (for better and/or for worse).


> Hadley

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