How to check if instance of `R6` class is present in a vector of class instances

Question

I am looking for a way to check if a given instance of R6 class is present in a vector of R6 class instances.

library(R6)

# define a class
Person <- R6Class("Person", list(
  name = NULL,
  initialize = function(name) self$name <- name
))

# create two instances of a class
Jack <- Person$new(name = "Jack")
Jill <- Person$new(name = "Jill")

I naively used %in% to check this, and it seems to have worked:

# yes
c(Jack) %in% c(Jack, Jill)
#> [1] TRUE

But it actually returns TRUE no matter the instance:

# also yes
c(Jack) %in% c(Jill)
#> [1] TRUE

So I had two questions:

1. What is %in% actually matching that it always returns TRUE?
2. How can I correctly check if an instance of R6 class is present in a vector of class instances?

Answer 1

R6 objects are environments, c(Jack) is a list containing an environment and %in% acts like this on lists of environments.

e1 <- new.env()
e2 <- new.env()
list(e1) %in% list(e2)
## [1] TRUE

Try identical

sapply(c(Jack , Jill), identical, Jack)
## [1]  TRUE FALSE

R6 objects have "R6" in their class vector so

sapply(c(Jack, Jill, sin, 37), inherits, "R6")
## [1]  TRUE  TRUE FALSE FALSE