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

You can create a missing object by using substitute() without argument.

In your case we could make round1 a missing object in the else clause :

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

bar = function(b) {
  if(b > 10) round1=T else round1 <- substitute()
  foo(b, round1)
}

bar(9)
#> [1] 28.27433

^{Created on 2019-10-24 by the reprex package (v0.3.0)}