invisible attributes

invisible_attributes.R

set_invisible_attr <- function(x, ...) {
  x_chr <- as.character(substitute(x))
  pf <- parent.frame()
  if(bindingIsActive(x_chr, pf)) {
    env <- environment(activeBindingFunction(x_chr, pf))
    args <- list(...)
    env$closure$attrs[names(args)] <- args
    return(x)
  }
  closure <- new.env()
  closure$attrs <- list(...)
  closure$value <- x
  rm(list = x_chr, pos = pf)
  makeActiveBinding(x_chr, env = pf, function (v) {
    if(missing(v)) return(closure$value)
    closure$value <- v
    invisible(closure$value)
  })
  invisible(NULL)
}

invisible_attr <- function(x,  which) {
  x_chr <- as.character(substitute(x))
  pf <- parent.frame()
  if(!bindingIsActive(x_chr, pf)) return(NULL)
  env <- environment(activeBindingFunction(x_chr, pf))
  env$closure$attrs[[which]]
}

foo <- bar <- 42
set_invisible_attr(foo, evil = 666)
identical(foo, bar)
foo <- bar <- 43
invisible_attr(foo, "evil")
invisible_attr(bar, "evil")
identical(foo, bar)