R Programming By Example

The S3 object model

As you may recall, the R language is derived from the S language. S's object model evolved over time, and its third version introduced class attributes, which allowed for the S3 object model we find in R today. It is still the object model in R, and most of R's own built-in classes are of the S3 type. It's a valid and very flexible object model, but it's very different from what people who come from other object-oriented languages are used to.

S3 is the least formal object model, so it's lacking in some key respects. For example, S3 does not offer formal class definitions, which implies that there's no formal concept of inheritance or encapsulation, and polymorphism is achieved through generics. It's clear that its functionality ...