r - setRefClass 按值传递，按引用传递

Question

我怀疑我不了解setRefClassR 中的所有方面。假设我有一个setRefClass初始化的实例。我想创建变量X，以便该变量等于实例的副本或引用setRefClass. 有没有区别：

x = InstanceOfsetRefClass

和

x <<- InstanceOfsetRefClass

我不完全理解，我的代码似乎有奇怪的行为。

谢谢你的帮助

Answer 1

I don't think your problem is anything to do with reference classes, rather it's about scope. Consider the following example. We start by removing all variables from our workspace and create a definition for A:

rm(list=ls())
A = setRefClass("A", fields=list(x="numeric"))

Next we create and call the function f:

f = function() {
  x1 = 1
  a1 = A$new(x=10)
  x2 <<- 2
  a2 <<- A$new(x=10)
}
f()

The key difference between <<- and = is

The operators '<<-' and '->>' are normally only used in functions, and cause a search to made through parent environments for an existing definition of the variable being assigned. If such a variable is found (and its binding is not locked) then its value is redefined, otherwise assignment takes place in the global environment.

From the help page: ?"<<-"

So variables created using = aren't found in the global enviroment

R> x1
Error: object 'x1' not found
R> a1
Error: object 'a1' not found

but the other variables are:

R> x2
[1] 2
R> a2
Reference class object of class "A"
Field "x":
[1] 10