R: Match supplied arguments to function definition

call_match {rlang}

R Documentation

Match supplied arguments to function definition

Description

call_match() is like match.call() with these differences:

It supports matching missing argument to their defaults in the function definition.
It requires you to be a little more specific in some cases. Either all arguments are inferred from the call stack or none of them are (see the Inference section).

Usage

call_match(
  call = NULL,
  fn = NULL,
  ...,
  defaults = FALSE,
  dots_env = NULL,
  dots_expand = TRUE
)

Arguments

`call`	A call. The arguments will be matched to `fn`.
`fn`	A function definition to match arguments to.
`...`	These dots must be empty.
`defaults`	Whether to match missing arguments to their defaults.
`dots_env`	An execution environment where to find dots. If supplied and dots exist in this environment, and if `call` includes `...`, the forwarded dots are matched to numbered dots (e.g. `..1`, `..2`, etc). By default this is set to the empty environment which means that `...` expands to nothing.
`dots_expand`	If `FALSE`, arguments passed through `...` will not be spliced into `call`. Instead, they are gathered in a pairlist and assigned to an argument named `...`. Gathering dots arguments is useful if you need to separate them from the other named arguments. Note that the resulting call is not meant to be evaluated since R does not support passing dots through a named argument, even if named `"..."`.

Inference from the call stack

When call is not supplied, it is inferred from the call stack along with fn and dots_env.

call and fn are inferred from the calling environment: sys.call(sys.parent()) and sys.function(sys.parent()).
dots_env is inferred from the caller of the calling environment: caller_env(2).

If call is supplied, then you must supply fn as well. Also consider supplying dots_env as it is set to the empty environment when not inferred.

Examples

# `call_match()` supports matching missing arguments to their
# defaults
fn <- function(x = "default") fn
call_match(quote(fn()), fn)
call_match(quote(fn()), fn, defaults = TRUE)

[Package rlang version 1.0.2 Index]