r - 依赖于其他参数的匹配参数的最佳实践

Question

我是 R 函数的新手，到目前为止我会检查如下参数:

foo = function(state = c("solid", "liquid"),
               thing = c("rock", "water")) {
  
  state = match.arg(state)
  thing = match.arg(thing)
  
  if (state == "solid" & thing == "water") {
    stop("thing can't be water if state is solid!")
  }
  
  if (state == "liquid" & thing == "rock") {
    stop("thing can't be rock if state is liquid!")
  }
  
}

foo("solid", "brick")
#> Error in match.arg(thing): 'arg' deve ser um dentre "rock", "water"

foo("solid", "water")
#> Error in foo("solid", "water"): thing can't be water if state is solid!

foo("liquid", "rock")
#> Error in foo("liquid", "rock"): thing can't be rock if state is liquid!

创建于 2020-06-28 由 reprex package (v0.3.0)
但是在使用多个 args 时似乎需要做很多工作。
我看了assetthat和 checkmate包，但我不清楚什么是 正确或标准 方法来做到这一点。

Answer 1

我建议使用 allowlist或 denylist ，取决于哪个较短(您将有多少异常(exception))，但您必须以某种方式对它们进行硬编码。
例如:

foo = function(state = c("solid", "liquid", "both"),
               thing = c("rock", "brick", "water", "either")) {
  
  state = match.arg(state)
  thing = match.arg(thing)

  state_denylist <- list(
    solid = "water",
    liquid = c("rock", "brick")
  )

  if (thing %in% state_denylist[[state]]) {
    stop("thing cannot be ", sQuote(thing), " if state is ", sQuote(state))
  }
 
}

或者，如果定义允许的组合更容易，那么也许 state_allowlist并相应地更改您的逻辑( ... && ! thing %in% ... )。