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When we are using R6 objects and want to introduce some C++ code in our
project, we may also want to interact with these objects using Rcpp. With
this objective in mind, the key to interacting with R6 objects is that
they are essentially environments, and so they can be treated as such.
In this example, we will define a ‘Person’ class with some private attributes
and public methods. It will allow us to show how to create R6 objects in C++
and how to interact with them.
Creating a dummy R6 class
First, we define the class ‘Person’, with a name, an id, an item and some
With this simple class, we will be able to create R6 objects, initialize them
and call some of their methods.
Creating R6 objects in C++
To create R6 objects, we must first get the ‘new’ function that initializes
them. In this case, given that we have loaded the Person class into the
global environment, we will get it from there:
The previous example initializes a list with Persons. It is important to notice
that the only function relevant to us from the global environment is the ‘new’
function created by the R6 class. All the functions defined inside Person will
be contained in each instance of the class.
If the R6 object is defined inside some package, included our own package if
we are developing one, we must get it from there. To do this, the previous
function has to be modified as follows:
Calling the methods of an instance
Once we have instantiated an R6 object as an environment, we can call its
methods after getting them from the instance:
Note that if we are creating multiple instances, we have to get the desired
method from each one of them.
Private attributes and methods cannot be accessed in this manner, trying to do
so results in an error:
The error is telling us that there is no function called “bad_foo” in
the environment of the object “new_p”. In that environment, only public
attributes and methods are present on the surface. Theoretically, we could
still try to find the private attributes and methods inside the object, but
it goes against the paradigm and it would be much easier to just make
the method we want to call public.
Passing down R6 objects
Passing R6 objects as arguments to C++ functions is also straight forward
by treating them as environments:
clone: function (deep = FALSE)
get_id: function ()
get_name: function ()
give_item: function (item)
good_foo: function ()
initialize: function (name, id)
bad_foo: function ()
Note that there is no need to return the object, as the environment is passed
by reference and changes inside it will be reflected outside the function.
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