r - 有没有办法将 R6 对象分配给 S4 对象槽？

Question

正如主题所描述的，我正在寻找一种方法来实现这一目标:

require("R6")
R6cls <- R6::R6Class("R6obj",
    public = list(val = 1, foo = function() "foo!")
)
# check this R6 class
r6o <- R6cls$new()
r6o

# <R6obj>
#  Public:
#    clone: function (deep = FALSE) 
#    foo: function () 
#    val: 1

# now the S4 part 
S4wR6slot <- function() new("S4wR6slot")
setClass("S4wR6slot", contains = "environment", # or maybe "R6" or "R6cls"? tried them all but none seemed to work
         slots = list(a = "R6cls", b = "character"))
   
# Currently gives
Warning message:
undefined slot classes in definition of "S4wR6slot": a(class "R6cls") 
# but you can still kind of use it 
s4r6 <- S4wR6slot()
s4r6

# An object of class "S4wR6slot"
# <environment: 0x00000179de2da628>
# Slot "a":
# NULL
#
# Slot "b":
# character(0)
s4r6@b <- "text" # works nicely 
# BUT trying to assign to that env slot 
s4r6@a <- r6o

# will throw these "ugly" errors 
Error in (function (cl, name, valueClass)  : 
  c("assignment of an object of class “R6obj” is not valid for @‘a’ in an object of class “S4wR6slot”; is(value, \"R6cls\") is not TRUE", 
"assignment of an object of class “R6” is not valid for @‘a’ in an object of class “S4wR6slot”; is(value, \"R6cls\") is not TRUE")

使用setOldClass()也没有什么好处。 也许根本没有办法做到这一点——只是询问某人是否有想法？或者甚至可能实现了这一点 - 否则也许我的 rtfm 做得不够好，有人可以向我指出文档，其中说你不应该尝试使这项工作起作用？

Answer 1

有一种方法可以在 S4 类中包含 R6 对象，但涉及通过定义名为“R6”的 S4 类来欺骗 S4 系统。这将防止 methods 包提示类 R6 不存在。幸运的是，它实际上并没有检查原型(prototype)中的“R6”对象是否是 S4 类型，因此您可以将实际的 R6 对象粘贴在那里。

library(R6)

R6cls <- R6::R6Class("R6obj",
                     public = list(val = 1, foo = function() "foo!")
)

setClass('R6')

setClass("S4wR6slot", slots = list(a = 'R6', b = "character"),
         prototype = list(a = R6cls$new(), b = 'Hello'))

S4wR6slot <- function() new("S4wR6slot")

myS4 <- S4wR6slot()

class(myS4)
#> [1] "S4wR6slot"
#> attr(,"package")
#> [1] ".GlobalEnv"

isS4(myS4)
#> [1] TRUE

myS4@a
#> <R6obj>
#>   Public:
#>   clone: function (deep = FALSE) 
#>     foo: function () 
#>       val: 1