Читать книгу The Big R-Book - Philippe J. S. De Brouwer - Страница 211

Most programming languages implement an OO system where class definitions are created when the code is compiled and instances of classes are created at runtime. During runtime, it is not possible to change the class definitions.

However, R is an interpreted language that is interactive and functional. The consequence is that it is possible to change class definitions at runtime (“while working in the R-terminal”). So it is possible to call setClass() again with the same object name, and R will assume that you want to change the previously defined class definition and silently override it. This can lead, for example, to the situation where different objects pretend to be of the same class, while they are not.