Passing missing argument from function to function in R

Question

I’ve learned that it’s common practice to use optional arguments in function and check them with missing() (e.g. as discussed in SO 22024082)

In this example round0

Answer 1

rlang provides also a function missing_arg() that makes an argument be missing.

foo = function(a, round0) {
  a = a * pi
  if(!missing(round0)) round(a)
  else a
}

bar = function(b) {
  if(b > 10) round1 <- TRUE else round1 <- rlang::missing_arg()
  foo(b, round1)
}

foo(9)
#> [1] 28.27433
bar(9)
#> [1] 28.27433

^{Created on 2020-12-02 by the reprex package (v0.3.0)}