Set a functions environment to that of the calling environment (parent.frame) from within function

问题

I am still struggling with R scoping and environments. I would like to be able to construct simple helper functions that get called from my 'main' functions that can directly reference all the variables within those main functions - but I don't want to have to define the helper functions within each of my main functions.

helpFunction<-function(){
#can I add a line here to alter the environment of this helper function to that of the calling function?
return(importantVar1+1)
}

mainFunction<-function(importantVar1){
return(helpFunction())
}

mainFunction(importantVar1=3) #so this should output 4

回答1:

Well, a function cannot change it's default environment, but you can use eval to run code in a different environment. I'm not sure this exactly qualifies as elegant, but this should work:

helpFunction<-function(){
    eval(quote(importantVar1+1), parent.frame())
}

mainFunction<-function(importantVar1){
    return(helpFunction())
}

mainFunction(importantVar1=3)

回答2:

If you declare each of your functions to be used with dynamic scoping at the beginning of mainfunction as shown in the example below it will work. Using helpFunction defined in the question:

mainfunction <- function(importantVar1) {

    # declare each of your functions to be used with dynamic scoping like this:
    environment(helpFunction) <- environment()

    helpFunction()
}

mainfunction(importantVar1=3)

The source of the helper functions themselves does not need to be modified.

By the way you might want to look into Reference Classes or the proto package since it seems as if you are trying to do object oriented programming through the back door.

回答3:

The R way would be passing function arguments:

helpFunction<-function(x){ 
#you can also use importantVar1 as argument name instead of x
#it will be local to this helper function, but since you pass the value
#it will have the same value as in the main function
  x+1
}

mainFunction<-function(importantVar1){
  helpFunction(importantVar1)
}

mainFunction(importantVar1=3)
#[1] 4

Edit since you claim it "doesn't work":

helpFunction<-function(importantVar1){ 
  importantVar1+1
}

mainFunction<-function(importantVar1){
  helpFunction(importantVar1)
}

mainFunction(importantVar1=3)
#[1] 4

来源：https://stackoverflow.com/questions/23890522/set-a-functions-environment-to-that-of-the-calling-environment-parent-frame-fr

标签

function

environment-variables

scoping