match.args()

gistfile1.txt

``` r
matched.arg <- function(...) {
  c(...)[1]
}

match.args <- function() {
  formal.args <- formals(sys.function(sysP <- sys.parent()))
  formal.args <- Filter(function(x) is.call(x) && identical(x[[1]], as.name("matched.arg")), formal.args)
  env <- sys.frame(sysP)
  for (arg in names(formal.args)) {
    choices <- eval(do.call(substitute, list(formal.args[[arg]], list(matched.arg = quote(c)))), env)
    arg <- get(arg, parent.frame())
    match.arg(arg, choices)
  }
}

fun1 <- function(arg = matched.arg("foo", "bar"), y = 1) {
  match.args()
  arg
}
fun1()
#> [1] "foo"
fun1("foo")
#> [1] "foo"
fun1("bar")
#> [1] "bar"
fun1("baz")
#> Error in match.arg(arg, choices): 'arg' should be one of "foo", "bar"

fun2 <- function(arg = c("foo", "bar"), y = 1) {
  arg <- match.arg(arg)
  arg
}
fun2()
#> [1] "foo"
fun2("foo")
#> [1] "foo"
fun2("bar")
#> [1] "bar"
fun2("baz")
#> Error in match.arg(arg): 'arg' should be one of "foo", "bar"

# strangely fun1() is 3 times slower with reprex but same performance in the console, something about the stack maybe
bench::mark(fun1(), fun2(), min_time = 2, max_iterations = 100000)
#> # A tibble: 2 × 6
#>   expression      min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 fun1()       9.92µs  10.78µs    90760.    13.8KB     52.7
#> 2 fun2()       2.38µs   2.71µs   365258.        0B     54.8
bench::mark(fun1("foo"), fun2("foo"), min_time = 2, max_iterations = 100000)
#> # A tibble: 2 × 6
#>   expression       min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr>  <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 fun1("foo")   9.47µs  10.33µs    94932.        0B     56.0
#> 2 fun2("foo")   3.12µs   3.48µs   283473.        0B     62.4
bench::mark(fun1("bar"), fun2("bar"), min_time = 2, max_iterations = 100000)
#> # A tibble: 2 × 6
#>   expression       min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr>  <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 fun1("bar")   9.51µs  10.29µs    95722.        0B     56.5
#> 2 fun2("bar")   3.16µs   3.44µs   284578.        0B     62.6
```

<sup>Created on 2022-03-25 by the [reprex package](https://reprex.tidyverse.org) (v2.0.1)</sup>