r - 当需要清除状态时，如何优雅地处理R中的错误？

Question

最好的方法是处理R中的错误？我希望既可以从脚本的最终用户那里提取堆栈跟踪信息，又可以清理我可能正在使用的所有临时变量和状态。

所以我想我的问题有两个方面:

最重要的是，在处理错误时如何正确处理清理状态？

如何从R的错误消息中提取有用的有用信息，而无需内部
东西被吐出来吗？

此刻，我有一些类似的东西，但是(1)看起来非常糟糕，(2)仍然给我带来了可怕的错误消息。

# Create some temporary working state and variables to clean up
file <- "somefile"
working.dir <- getwd()
setwd("../")  # Go somewhere else
saf.default <- getOption("stringsAsFactors")
options(stringsAsFactors = FALSE)

# Now lets try to open the file, but it doesn't work (for whatever reason)
# I want to clean up the state, stop, and wrap the error string with a nicer
# message
tryCatch({
  # Need to embed the tryCatch because we still need some of the state variables
  # for the error message
  tryCatch({
    f <- read.table(file)
  }, error = function(err.msg) {
    # Can't clean up here, we still need the `file variable!
    stop("Could not open file '", file, "' with error message:\n", print(err.msg), 
         call.=FALSE)
  })
}, error = function(err.msg) {
  # Now we can clean up state
  setwd(working.dir)
  options(stringsAsFactors = saf.default)
  rm(file, working.dir, saf.default, 
     envir=globalenv())  # This also seems awful?
  stop(print(err.msg), call.=FALSE)
})

# Do more stuff, get more state, handle errors, then clean up.
# I.e can't use `finally` in previous tryCatch!

由此产生的错误消息仍然是许多丑陋的内部结构:

# <simpleError in file(file, "rt"): cannot open the connection>
# <simpleError: Could not open file 'somefile' with error message:
# Error in file(file, "rt"): cannot open the connection
>
# Error: Could not open file 'somefile' with error message:
# Error in file(file, "rt"): cannot open the connection
# In addition: Warning messages:
# 1: In file(file, "rt") :
#   cannot open file 'somefile': No such file or directory
# 2: In stop(print(err.msg), call. = FALSE) :
#   additional arguments ignored in stop()
>

Answer 1

我会将任何状态更改代码隔离到其自己的函数中，并使用on.exit。这保证了清除将发生，无论是否发生错误。

readFile <- function(.....)
{
    on.exit({
        setwd(cur.dir)
        options(stringsAsFactors=saf)
    })
    cur.dir <- getwd()
    saf <- getOption("stringsAsFactors")
    setwd("new/dir")
    options(stringsAsFactors=FALSE)
    ....
}