conflicting note on global variable assignment

[krishnakeshav]

lintr gives conflicting notes for scenario below -

library(utils)
utils::globalVariables(c("g_var"))

test_gvar <- function() {
  g_var <- 5
}
print(g_var)

It's likely for variable to be used outside the function when I have already declared it to be global with utils::globalVariables(c("g_var"))
It should have been resolved as per this.

[MichaelChirico]

is this part of a script or a package?

[krishnakeshav]

@MichaelChirico

is this part of a script or a package?

Issue originally occurred in a package, but the above example is a script for the sake of reproducing.
The easiest way around this is to add return(g_var).

[AshesITR]

Your code doesn't do what you think it does, and the warning is justified.

If you want to overwrite g_var in the outer scope from within the function, you need to use <<-.

[krishnakeshav]

Your code doesn't do what you think it does, and the warning is justified.

If you want to overwrite g_var in the outer scope from within the function, you need to use <<-.

using <<- in conjunction to glovalVariables also gives warning, see below -

It seems to me that <<- is not recognized as an operator to lint.

[AshesITR]

Sorry for being unclear.
You should of course also define the global variable before writing to it.

[krishnakeshav]

Sorry for being unclear. You should of course also define the global variable before writing to it.

Thanks @AshesITR , it works well with scripts. In package, when I run lint active package from R studio, I don't get any notes. However, upon running R CMD check, I get the note as below -

no visible binding for '<<-' assignment to ‘result_index_list’

Note that, I have different code in case of R script in package.

result_index_list <<- NULL
some_fun <- function() {
  result_index_list <<- some_list_assignment
}

In above, if I use result_index_list <- NULL, then I get following runtime error -

Error in FUN(X[[i]], ...) :
cannot change value of locked binding for 'result_index_list'

I have R/globals.R with utils::globalVariables(c("result_index_list"))
Does lint behave differently in R CMD check than the scripts ?

[AshesITR]

@krishnakeshav I recommend you read the R Packages section on internal state for packages to see how you should define and use global state in Packages.

Here is a MWE copied from there:

the <- new.env(parent = emptyenv())
the$favorite_letters <- letters[1:3]

#' Report my favorite letters
#' @export
mfl2 <- function() {
  the$favorite_letters
}

#' Change my favorite letters
#' @export
set_mfl2 <- function(l = letters[24:26]) {
  old <- the$favorite_letters
  the$favorite_letters <- l
  invisible(old)
}

For plain scripts, the error "cannot change value of locked binding ..." will disappear.

[krishnakeshav]

@krishnakeshav I recommend you read the R Packages section on internal state for packages to see how you should define and use global state in Packages.

Here is a MWE copied from there:

the <- new.env(parent = emptyenv())
the$favorite_letters <- letters[1:3]

#' Report my favorite letters
#' @export
mfl2 <- function() {
  the$favorite_letters
}

#' Change my favorite letters
#' @export
set_mfl2 <- function(l = letters[24:26]) {
  old <- the$favorite_letters
  the$favorite_letters <- l
  invisible(old)
}

For plain scripts, the error "cannot change value of locked binding ..." will disappear.

This worked for me. Thanks again @AshesITR