r - 在定义中使用省略号时如何在 R 函数调用中捕获错误或未定义的参数

Question

我正在努力解决一个公认的问题，但我还没有找到一个简单的解决方案:当函数定义包含省略号或三个点时，如何捕获传递给 R 函数的错误指定参数 ... .

正如 Wickham 的 Advanced R 中所述:

Using ... comes at a price — any misspelled arguments will not raise an error, and any arguments after ... must be fully named. This makes it easy for typos to go unnoticed.

下面是一个例子:

myfun <- function(x, ...) 
    UseMethod("myfun")

myfun.character <- function(x, toLower = FALSE, ...)
    cat("Sent and transformed by myfun:", ifelse(toLower, tolower(x), x), "\n")

myfun("Test String with CaPiTaLs.")
## Sent and transformed by myfun: Test String with CaPiTaLs.
myfun("Test String with CaPiTaLs.", toLower = TRUE)
## Sent and transformed by myfun: test string with capitals. 
myfun("Test String with CaPiTaLs.", tolower = TRUE)
## Sent and transformed by myfun: Test String with CaPiTaLs.
myfun("Test String with CaPiTaLs.", toLower = TRUE, notDefined = 1)
## Sent and transformed by myfun: test string with capitals. 

在这里， toLower 的微妙拼写错误正如用户可能预期的那样，除了输出为小写失败之外，不会导致任何可见错误。在最后一个例子中，用户认为有用的参数不是，但由于 ... 的性质，它们只是消失在以太中。 .

当然我可以查看 ...的内容通过 list(...) ，但我想知道是否有更好的方法，链接到函数中定义的形式或那些 ...通过。

顺便说一句，有谁知道我们应该怎么称呼 ... ?我几乎可以肯定我在 Julia 文档中看到了一个带有名称的引用，但现在找不到了!

补充:

理想情况下，当被调用函数范围内的某些内容通过省略号传递给辅助参数时，如果参数不是应该在省略号中传递的内容，我想找出生成错误的最佳方法。例如，如何最好地捕获这些错误:

myfun2 <- function(x, ...) 
    UseMethod("my fun")

myfun2.character <- function(x, toLower = FALSE, ...)
    cat("Sent and transformed by myfun:", ifelse(toLower, tolower(x), x), "\n", ...)

myfun2("Test String with CaPiTaLs.", tolower = TRUE)
## Sent and transformed by myfun: Test String with CaPiTaLs. 
##  TRUE
myfun2("Test String with CaPiTaLs.", toLower = TRUE, notDefined = 1)
## Sent and transformed by myfun: test string with capitals. 
##  1
myfun2("Test String with CaPiTaLs.", sep = "\tXX\t")
## Sent and transformed by myfun:   XX  Test String with CaPiTaLs.  XX  

Answer 1

我不会返回错误。一个警告就足够了。像这样的东西:

myfun2.character <- function(x, toLower = FALSE, ...) {
  elli <- names(list(...))
  check <- elli %in% names(formals(cat))
  if (any(!check)) warning(sprintf("%s is not an expected parameter. Did you misstype it?", 
                                   paste(elli[!check], collapse = ", ")))
  cat("Sent and transformed by myfun:", ifelse(toLower, tolower(x), x), "\n", ...)
}


myfun2("Test String with CaPiTaLs.", tolower = TRUE)
#Sent and transformed by myfun: Test String with CaPiTaLs. 
#TRUE
#Warning message:
#  In myfun2.character("Test String with CaPiTaLs.", tolower = TRUE) :
#  tolower is not an expected parameter. Did you misstype it?
myfun2("Test String with CaPiTaLs.", toLower = TRUE, notDefined = 1)
#Sent and transformed by myfun: test string with capitals. 
#1
#Warning message:
#  In myfun2.character("Test String with CaPiTaLs.", toLower = TRUE,  :
#                        notDefined is not an expected parameter. Did you misstype it?
myfun2("Test String with CaPiTaLs.", sep = "\tXX\t")
## Sent and transformed by myfun:   XX  Test String with CaPiTaLs.  XX

我不认为最后一个应该警告。无论如何你应该避免位置参数匹配，如果你在那里使用名称匹配，你会得到一个错误，你需要捕获。