Defining indexing operations

An object that is a Course class can have many assignment objects in its Grades slot. We did not define a special method to get a particular assignment, and no method is defined to save an assignment. We examine how to do this is in this section, and the discussion revolves around redefining the [ operation.

First we redefine the [ operation used to get an assignment. The idea is that we want to get a copy of an assignment by enclosing the name of the assignment as defined in the original file within square braces. To do this, we can redefine the operation. In this case, we want to be able to pass any kind of object within the braces, which will allow us to also use integers to index by location in the list:

setMethod("[",
          signature(x="Course",i="ANY"),
          definition=function(x,i=1)
          {
              #print(paste("Get grade item",i))
              return(x@Grades[[i]])
          }
          )

We would...