扩展tibble:让新的S3类保持不变

为了 ropensci/drake#489 ,我想为 tibbles 阶级的 "drake_plan" . 我读了 guide on extending tibble ,这对某些需求很有帮助。但是新的 “德雷克计划” S3课程在 dplyr 操作。

#' @title Mark a data frame as a `drake` workflow plan
#' @description Used for pretty printing only (coming soon).
#'   You do not actually have to mark plans as such.
#'   You can keep them as ordinary data frames.
#' @export
#' @keywords internal
#' @param x object to mark as a `drake` plan
#' @param ... other arguments to the method
#' @examples
#' plan <- list(target = "x", command = "get_data()")
#' class(plan)
#' plan <- as_drake_plan(plan)
#' class(plan)
as_drake_plan <- function(x){
  UseMethod("as_drake_plan")
}

as_drake_plan_ <- function(x, ...){
  tibble::new_tibble(x, ..., subclass = "drake_plan")
}

#' @export
`[.drake_plan` <- function(...){
  as_drake_plan_(NextMethod())
}

#' @export
#' @rdname as_drake_plan
as_drake_plan.data.frame <- as_drake_plan_

#' @export
#' @rdname as_drake_plan
as_drake_plan.list <- as_drake_plan_

#' @export
#' @rdname as_drake_plan
as_drake_plan.tbl_df <- as_drake_plan_

library(dplyr)
library(drake)
plan <- drake_plan(
  x = get_data(),
  y = analyze_data(x)
) %>%
  as_drake_plan() %>%
  print
#> # A tibble: 2 x 2
#>   target command        
#> * <chr>  <chr>          
#> 1 x      get_data()     
#> 2 y      analyze_data(x)
class(plan)
#> [1] "drake_plan" "tbl_df"     "tbl"        "data.frame"
filter(plan, target == "x") %>%
  class()
#> [1] "tbl_df"     "tbl"        "data.frame"

而且 dplyr公司 函数,是否有其他情况可以从 藏 s?