r - 更新 R 中三点省略号的值

Question

我有一个功能 foo()我希望能够以两种不同的“模式”调用:一次或在 while 循环中。

我想使用一个有点通用的包装器( runtime_gateway() )并通过 ... 传递参数至 foo()在这里很有意义，所以我可以利用相同的“运行时网关逻辑”来处理具有不同参数集的任意函数。

如果运行 foo()在while循环中，我想更新一些 其参数的同时 保持其他参数的默认值或传递值。

我该怎么做？

我知道 rlang::dot_list(...)和 friend ，快速浏览了 https://github.com/r-lib/ellipsis .似乎其中任何一个只会让从省略号内容中提取值或检查省略号内容，但我不知道如何“在传输中更新它”。

正品

foo <- function(
  id = "id_a",
  at = Sys.time()
) {
  message(stringr::str_glue("{id}: {at}"))
  Sys.sleep(1)
}

runtime_gateway <- function(
  fun = foo,
  run_mode = c("once", "while"),
  ... # Args to be passed to `fun`
) {
  run_mode <- match.arg(run_mode)

  if (run_mode == "once") {
    fun(...)
  } else if (run_mode == "while") {
    counter <- 0

    while(counter < 3) {
      # Goal: keep ellipsis value for `id` but *update* value for `at`
      dots <- rlang::dots_list(...)
      at <- if ("at" %in% names(dots)) {
        message("`at` was passed via ellipsis:")
        message(dots$at)
        dots$at
      } else {
        Sys.time()
      }

      fun(at = at + 60, ...)
      counter <- counter + 1
    }
  }
}

runtime_gateway()
#> id_a: 2020-02-21 14:09:16.779
runtime_gateway(at = lubridate::ymd_hms("2020-02-21 10:30:00"))
#> id_a: 2020-02-21 10:30:00

runtime_gateway(run_mode = "while")
#> id_a: 2020-02-21 14:10:18.897
#> id_a: 2020-02-21 14:10:19.900
#> id_a: 2020-02-21 14:10:20.902
runtime_gateway(run_mode = "while", id = "id_b")
#> id_b: 2020-02-21 14:10:21.905
#> id_b: 2020-02-21 14:10:22.906
#> id_b: 2020-02-21 14:10:23.908
runtime_gateway(run_mode = "while", at = lubridate::ymd_hms("2020-02-21 10:30:00"))
#> `at` was passed via ellipsis:
#> 2020-02-21 10:30:00
#> Error in fun(at = at + 60, ...): formal argument "at" matched by multiple actual arguments

创建于 2020-02-21 由 reprex package (v0.3.0)

Answer 1

您可以确保 dots包含 at如果不存在则添加参数，然后调度 fun使用 dots而不是 ...与 do.call

runtime_gateway <- function(
  fun = foo,
  run_mode = c("once", "while"),
  ... # Args to be passed to `fun`
) {
  run_mode <- match.arg(run_mode)

  if (run_mode == "once") {
    fun(...)
  } else if (run_mode == "while") {
    counter <- 0

    while(counter < 3) {
      # Goal: keep ellipsis value for `id` but *update* value for `at`
      dots <- rlang::dots_list(...)
      if ("at" %in% names(dots)) {
        message("`at` was passed via ellipsis:")
        message(dots$at)
        dots$at <- dots$at + 60
      } else {
        dots$at <- Sys.time() + 60
      }

      do.call(fun, dots)
      counter <- counter + 1
    }
  }
}

这是输出:

runtime_gateway()
#> id_a: 2020-02-21 14:22:07

runtime_gateway(at = lubridate::ymd_hms("2020-02-21 10:30:00"))
#> id_a: 2020-02-21 10:30:00

runtime_gateway(run_mode = "while")
#> id_a: 2020-02-21 14:23:09
#> id_a: 2020-02-21 14:23:10
#> id_a: 2020-02-21 14:23:11

runtime_gateway(run_mode = "while", id = "id_b")
#> id_b: 2020-02-21 14:23:12
#> id_b: 2020-02-21 14:23:13
#> id_b: 2020-02-21 14:23:14

runtime_gateway(run_mode = "while", at = lubridate::ymd_hms("2020-02-21 10:30:00"))
#> `at` was passed via ellipsis:
#> 2020-02-21 10:30:00
#> id_a: 2020-02-21 10:31:00
#> `at` was passed via ellipsis:
#> 2020-02-21 10:30:00
#> id_a: 2020-02-21 10:31:00
#> `at` was passed via ellipsis:
#> 2020-02-21 10:30:00
#> id_a: 2020-02-21 10:31:00

创建于 2020-02-21 由 reprex package (v0.3.0)