Implementing column name proxy for custom tibble class

col_proxy.R

library(dplyr)
library(rlang)
library(purrr)

x <- tibble(year=2011:2015,
             value=runif(5))

# extending the tibble class
class(x) <- unique(c("tbl_cf", class(x)))
attr(x, ".index") <- "year"

filter.tbl_cf<-function(x, ...){
  # capture the args and substitute the .index
  args_list <- quos(...) %>% 
    map(quo_name) %>% 
      map(~gsub(".index", attr(x, ".index"), .x)) %>% 
      map(~parse_quosure(.x)) 
  
  # strip the class to avoid infinite loop
  class(x) <- class(x)[-1]
  res <- x %>% 
    dplyr::filter(UQS(args_list))
  
  # restore the custom class
  res(x) <- unique(c("tbl_cf", class(x)))
}

filter(x, .index == 2015)

The idea is that user does not have to care what the key property of the object is called. So long that the class is maintained, methods should be able to interpret reference to feature class attribute.