advanced R（chapter7 environment）

basic question

• Environment vs list
• parent of the global environment?
• enclosing environment of a function
• determine the environment from which a function was called
• <- and <<- different?

Environment bisics

important environment

Access the global environment with globalenv() and the current environment with environment()

parent environment

Every environment has a parent
The parent is what’s used to implement lexical scoping: if a name is not found in an environment, then R will look in its parent (and so on)

e2a <- env(d = 4, e = 5)
e2b <- env(e2a, a = 1, b = 2, c = 3)
# e2a is the parent of e2b.

You can find the parent of an environment with env_parent():

env_parent(e2b)
#> <environment: 0x7fe6c7399f58>
env_parent(e2a)
#> <environment: R_GlobalEnv>

Super assignment, <<-

Super assignment, <<-, never creates a variable in the current environment, but instead modifies an existing variable found in a parent environment.

x <- 0
f <- function() {
  x <<- 1
}
f()
x
#> [1] 1
如果使用的是<-
x <- 0
f <- function() {
  x <- 1
}
f()
x
#> [1] 0