R scrambled argument order

weird.R

library(rlang)

fun <- function(x = 3, y, z = 1) {
    paste(x, y, z)
}

# default arguments and regular argument order can be scrambled
# yet produce the same call

# look at actual call
rlang::call_standardise(quote(fun(1, 2, 3)))
# fun(x = 1, y = 2, z = 3)
fun(1, 2, 3)
# [1] "1 2 3"

# look at actual call
rlang::call_standardise(quote(fun(2, x=1, 3)))
# fun(x = 1, y = 2, z = 3)
fun(2, x=1, 3)
# [1] "1 2 3"

# look at actual call
rlang::call_standardise(quote(fun(z=3, x=1, 2)))
# fun(x = 1, y = 2, z = 3)
fun(z=3, x=1, 2)
# [1] "1 2 3"