Recognition of a function input by filter in R?

Question

In my foo() call below, is there a way for the input of filter_var = (i.e., test) to be recognized inside the function?

Right now, the input is not recognized.

library(tidyverse)
library(rlang)

foo <- function(..., filter_var = NULL){

filter_var <- rlang::ensyms(filter_var)
  
dat <- expand_grid(...)  

dat %>%
filter(
  
    {{filter_var}} != "A"   ## HERE `filter_var` is not recognized. 
  )
}

foo(study = 1:2, test = LETTERS[1:2], filter_var = test)

#  study test 
#  <int> <chr>
#1     1 A    
#2     1 B    
#3     2 A    
#4     2 B 

Answer 1

You can't combine ensym and {{}}. Either use {{}} without the explict ensym

foo <- function(..., filter_var = NULL){
  dat <- expand_grid(...)  
  dat %>%
    filter({{filter_var}} != "A")
}

foo(study = 1:2, test = LETTERS[1:2], filter_var = test)

or use !! with the ensym (note that you're only decoding one symbol so use ensym rather than ensyms).

foo <- function(..., filter_var = NULL){
  filter_var <- rlang::ensym(filter_var)
  dat <- expand_grid(...)  
  dat %>%
    filter(!!filter_var != "A")
}