5.5 dot-dot-dot …

Use it to pass on arguments to another function inside.

But you can also use it to force named arguments in your function.

sum_3 <- function(x, y, z) {
  return(x + y + z)
}

sum_3(1, 2, 3)
## [1] 6

sum_3 <- function(x, y, ..., z) {
  return(x + y + z)
}

sum_3(1, 2, z = 3)
## [1] 6

sum_3(1, 2, z = 3)
## [1] 6