Pointers in R Programming Language

R does not have pointers in the same way as Go, but we can simulate similar behavior using environments. Here’s an example that demonstrates the concept:

# We'll show how environments work in contrast to values with
# 2 functions: `zeroval` and `zeroenv`. `zeroval` has an
# integer parameter, so arguments will be passed to it by
# value. `zeroval` will get a copy of `ival` distinct
# from the one in the calling function.

zeroval <- function(ival) {
  ival <- 0
}

# `zeroenv` in contrast has an environment parameter. 
# Assigning a value to a variable in the environment 
# changes the value in the referenced environment.

zeroenv <- function(ienv) {
  ienv$value <- 0
}

main <- function() {
  i <- 1
  cat("initial:", i, "\n")

  zeroval(i)
  cat("zeroval:", i, "\n")

  # Create an environment to hold our value
  ienv <- new.env()
  ienv$value <- i
  
  zeroenv(ienv)
  i <- ienv$value
  cat("zeroenv:", i, "\n")

  # Environments can be printed too.
  cat("environment:", capture.output(print(ienv)), "\n")
}

main()

zeroval doesn’t change the i in main, but zeroenv does because it has a reference to the environment that holds the variable.

When you run this script, you should see output similar to:

initial: 1
zeroval: 1
zeroenv: 0
environment: <environment: 0x55f4a9876c20>

In this R example, we use environments to simulate pointer-like behavior. The zeroenv function takes an environment as an argument and modifies the value stored in that environment. This is similar to how the zeroptr function in the original Go code modifies the value at a memory address.

Note that while this demonstrates a similar concept, R’s environments and Go’s pointers are fundamentally different. R uses lexical scoping and environments, which provide a different model for managing variable references compared to Go’s more direct memory manipulation with pointers.