Auto update of a field (data member) in R reference class

Any equivalent as the decorator @property in python?

That is to have one field automatically updated (on access) due to an update of another field, instead of recomputing it before access.

UPDATE 2014-02-06

By defining "one" field as an activeBindingFunction of "another" field turns on the automatic updates (See @jdharrison's answer). However, is there anyway to check whether such updates are lazy evaluation? If not, how can we achieve this?

(A later edit: an "informal" print function inside the activeBindingFunction is evident that the evaluation is lazy. Any way to check this issue in a more formal manner?)

For better illustration of my question, below is a piece of python code producing the desired lazy behavior via decorator @property - bear with me to put it in an R-tagged question.

class Test(object):
    def __init__(self):

    def num1(self):
        if (self._num1 is None):

    def num1(self, value):
        self._num1 = value

    def num2(self):

The interactive session

In [2]: obj=Test()

In [3]: obj.__dict__
Out[3]: {'_num1': None, '_num2': None}

In [4]: obj.num1
Out[4]: 1

In [5]: obj.__dict__
Out[5]: {'_num1': 1, '_num2': None}

In [6]: obj.num2
Out[6]: 2

In [7]: obj.__dict__
Out[7]: {'_num1': 1, '_num2': 2}

In [8]: obj.num1 = 5

In [9]: obj.__dict__
Out[9]: {'_num1': 5, '_num2': 2}

In [10]: obj.num2
Out[10]: 10

In [11]: obj.__dict__
Out[11]: {'_num1': 5, '_num2': 10}


Not sure if its what you are after

test <- setRefClass("test",
                            fields   = list(
                                            num1 = "numeric"
                                            , num2 = function(){
                            methods  = list(
                              initialize = function(num1 = 1){
                                num1 <<- num1

                              show = function(){
                                print(c(num1 = num1, num2 = num2))

> tt <- test()
> tt
[1] "hello;"
num1 num2 
   1    2 
> tt$num1<-4
> tt
[1] "hello;"
num1 num2 
   4    8 

Need Your Help

How to use output of a command inside an awk command?

bash variables awk pipe

I want to print out the last update of a log file and nothing above it (old logs). Every 5 minutes the log is updated/appended to, and there is no option to overwrite instead of append. The amount of

Create A Twitter Login Application

php twitter oauth

In the past few weeks I've been developing a custom PHP login class that I will share with the rest of the devs in just a matter of days or weeks, depending on how quick I'll move with what I'm abo...