R and object oriented programming

S3 classes

• Not really objects, more of a naming convention
• Based around the . syntax: E.g. for print, print calls print.lm print.anova, etc. And if not found,print.default

S4 classes

• Can dispatch on multiple arguments
• More complicated to implement than S3

Reference classes

• Primarily useful to avoid making copies of large objects (pass by reference)
• Description of reasons to use RefClasses

proto

• ggplot2 was originally written in proto, but will eventually be rewritten using S3.
• Neat concept (prototypes, not classes), but seems tricky in practice
• Next version of ggplot2 seems to be moving away from it
• Description of the concept and implementation

R6 classes

• By-reference
• Does not depend on S4 classes
• “Creating an R6 class is similar to the reference class, except that there’s no need to separate the fields and methods, and you can’t specify the types of the fields.”