R Reference | R Reference Class - r - learn r - r programming
- Reference class in R programming is similar to the object oriented programming we are used to seeing in common languages like C++, Java, Python etc.
- Defines and uses reference class objects.
- Unlike S3 and S4 classes, methods belong to class rather than generic functions.
- Reference class are internally implemented as S4 classes with an environment added to it.
r programming class object pass by reference
How to defined a reference class?
- Defining reference class is similar to defining a S4 class.
- Instead of setClass() we use the setRefClass() function.
- Member variables of a class, if defined, need to be included in the class definition.
- Member variables of reference class are called fields (analogous to slots in S4 classes).
- Following is an example to define a class called student with 3 fields, name, age and GPA.
How to create a reference objects?
- The function setRefClass() returns a generator function which is used to create objects of that class.
How to access and modify fields?
- Fields of the object can be accessed using the $ operator.
- Similarly, it is modified by reassignment.
- In R programming, objects are copied when assigned to new variable or passed to a function (pass by value).
- But this is not the case with reference objects. Only a single copy exist and all variables reference to the same copy. Hence the name, reference.
- This can make some unwanted change in values and be the source of strange bugs.
- We need to keep this in mind while working with reference objects.
- To make a copy, we can use the copy() method made availabe to us.
- Methods are defined for a reference class and do not belong to generic functions as in S3 and S4 classes.
- All reference class have some methods predefined because they all are inherited from the superclass envRefClass.
- We can see class methods like copy(), field() and show() in the above list.
- We can create our own methods for the class.
- This can be done during the class definition by passing a list of function definitions to methods argument of setRefClass().
- In the above section of our code, we defined two methods called inc_age() and dec_age(). These two method modify the field age.
- Note that we have to use the non-local assignment operator <<- since age isn't in the method's local environment.
- Using the simple assignment operator <- would have created a local variable called age, which is not what we want. R will issue a warning in such case.
- Here is a sample run where we use the above defined methods.