R/imapper.R

In interfacer: Define and Enforce Contracts for Dataframes as Function Parameters

#' Specify mappings that can make dataframes compatible with an `iface` specification
#' 
#' When a function uses [ivalidate()] internally to check a dataframe conforms to 
#' the input it can attempt to rescue an incorrectly formatted dataframe.
#' This is a pretty advanced idea and is not generally recommended.
#' 
#' This function is expected to be used only in the context of a `.imap = imapper(...)`
#' parameter to an [ivalidate()] call to make sure that certain columns are present
#' or are a set value. Anything provided here will overwrite existing
#' dataframe columns and its use is likely to make function behaviour obtuse. 
#' It may be deprecated in the future. The `...` input expressions should almost certainly 
#' check for the values already existing before overwriting them. 
#' 
#' If you are considering using this for replacing missing values check using
#' the `default(...)` `iface` type definition instead.
#'
#' @param ... a set of [dplyr::mutate()] specifications that when applied to
#' a dataframe will rename or otherwise fix missing columns
#'
#' @return a set of mappings
#' @export
#'
#' @concept interface 
#'
#' @examples
#' x = function(df = iface(col1 = integer ~ "an integer column" ), ...) {
#'   df = ivalidate(df,...)
#' }
#' input=tibble::tibble(col2 = c(1,2,3)) 
#' # This fails because col1 is missing
#' try(x(input))
#' # This fixes it for this input
#' x(input, .imap=imapper(col1 = col2))
imapper = function(...) {
  tmp = rlang::enexprs(...)
  return(structure(
    tmp,
    class = c("imapper",class(tmp))
  ))
}