从正式的函数论证中获取选择

Question

有没有办法访问函数参数的选择？

在这个愚蠢的例子中：

noise <- function(animal = c("dog","cat","chicken","pig")){ # default animal is "dog"
  animal <- match.arg(animal)
  sound <- c("woof","meow","cluck","oink")[match(animal, c("dog","cat","chicken","pig"))]
  sound
}
noise("chicken") # returns desired result

我想通过访问声明中的选项向量来避免重新输入c("dog","cat","chicken","pig")，类似于（制作此选项）：

noise <- function(animal = c("dog","cat","chicken","pig")){ 
      animal <- match.arg(animal)
      sound <- c("woof","meow","cluck","oink")[match(animal, self.choices("animal"))]
      sound
    }

Answer 1

试试这个：eval(formals(noise)[["animal"]])