如何在R中不执行函数的前提下获取其调用的参数名称？

To get the parameter names of a function without executing it, you need to pass the function object itself (not the result of calling it) to your helper function. Here's how to implement getArgNames:

testFun <- function(x = 1:20, z = list(a = 1, b = 2)) x %>% sin %>% sum

getArgNames <- function(value) {
  # Prevent accidental passing of function results instead of the function itself
  if (!is.function(value)) {
    stop("Input must be a function object, not the output of calling it!")
  }
  # Extract parameter names from the function's formal arguments
  names(formals(value))
}

# Correct usage: pass the function directly, not testFun()
arg.names <- getArgNames(testFun)
arg.names
# Output: [1] "x" "z"

Explanation #

1. Avoid executing the function: In your original example, testFun() runs the function and returns a numeric value. Instead, pass testFun (the function object) to getArgNames to skip execution entirely.

2. formals() function: This built-in R tool retrieves a function's formal arguments as a named list. For testFun, formals(testFun) returns:

   $x
   1:20
   
   $z
   list(a = 1, b = 2)
   

3. Extract parameter names: The names of this list are exactly the function's parameter names, so wrapping formals(value) in names() gives us the desired vector.

Edge Cases #

• Functions with no parameters: formals(function() {}) returns NULL, so getArgNames will return NULL (which is correct for a parameterless function).
• Functions with ... (dots): For a function like function(x, ...) {}, getArgNames will return c("x", "...").
• Primitive base functions: Some core R functions (like sum) are primitives that don't expose formals via formals(). For these, you can use args() instead: names(as.list(args(value)))[-1] (the [-1] removes the extra function( entry from the result).

内容的提问来源于stack exchange，提问作者Taz