如何在 R 中使用 `tryCatch` 正确记录警告和错误？

我有一个函数fun通常会产生警告，偶尔会引发错误。我正在尝试使用tryCatch记录警告和错误，如建议的那样这个答案 https://stackoverflow.com/a/57658252/5252007。如何同时存储警告和错误？

这是一个最小的设置：

# Function for warnings, errors.
fun <- function(i) {
    # Print warnings as they come in.
    options(warn = 1)

    # Issue warning.
    warning(paste("Warn.", i))

    # Stop.
    if(i == 3) { stop(paste("Err.", i)) }

    # Restore warning default behaviour.
    options(warn = 0)
}

评估fun with tryCatch:

# Storage
warns = list()
errs = list()

# Try catch the function and log the warnings/ errors.
for (i in 1:4) {
    tryCatch(fun(i),
        warning = function(w) warns[[i]] <<- w,
        error = function(e) errs[[i]] <<- e
    )
}

但是，输出显示错误尚未存储。

warns
# [[1]]
# <simpleWarning in fun(i): Warn. 1>
# 
# [[2]]
# <simpleWarning in fun(i): Warn. 2>
# 
# [[3]]
# <simpleWarning in fun(i): Warn. 3>
# 
# [[4]]
# <simpleWarning in fun(i): Warn. 4>


errs
# list()

基于Ronak's有用的评论和以下问题如何将警告和错误保存为函数的输出？ https://stackoverflow.com/q/4948361/5252007，代码可以简化如下：

# Storage.
warns = list()
errs = list()


# Example function.
fun <- function(i) {
    # Issue warning.
    warning(paste("Warn.", i))

    # Stop.
    if(i == 3) { stop(paste("Err.", i)) }
}


# Evaluate `fun`.
for (i in 1:4) {
    tryCatch(withCallingHandlers(
        expr = fun(i), 

        # Handle the warnings.
        warning = function(w) {
            warns <<- c(warns, list(w))
            invokeRestart("muffleWarning")
        }), 

        # Handle the errors.
        error = function(e) {
            errs <<- c(errs, list(e))
        }
    )
}

输出如下所示：

warns

# [[1]]
# <simpleWarning in fun(i): Warn. 1>
# 
# [[2]]
# <simpleWarning in fun(i): Warn. 2>
# 
# [[3]]
# <simpleWarning in fun(i): Warn. 3>
# 
# [[4]]
# <simpleWarning in fun(i): Warn. 4>


errs

# [[1]]
# <simpleError in fun(i): Err. 3>

更多信息和链接在question https://stackoverflow.com/q/4948361/5252007上面链接了。