r - 如何在 R 的闭包中查询符号的值？

Question

如何在下面的 R 代码中查询 foo 的 x 值？

make.foo <- function() {
    x <- 123
    function() x * 3
}

foo <- make.foo()

# now get foo's x

Answer 1

一个函数会有一个环境

来自 ?`function`

A closure has three components, its formals (its argument list), its body (expr in the ‘Usage’ section) and its environment which provides the enclosure of the evaluation frame when the closure is used.

因此您可以从该环境中获取(或使用ls 列出对象)

get('x', envir = environment(foo))
## [1] 123

或者如果你想知道环境中的所有对象

ls(envir = environment(foo))
## 'x'

如果你想分配给那个环境(即改变x)

assign('x', 24, envir = environment(foo))

foo()
## 72

你甚至可以将它从环境中移除

rm(x, envir = environment(foo))
foo()
## Error in foo() : object 'x' not found

然后使用全局分配的x

x <- 3
foo()
# [1] 9

并重新分配给函数的环境

assign('x', 123, envir = environment(foo))
foo()
## [1] 369