call_match {rlang}

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)