Get an optional function without triggering a CRAN warning

You want to use a function if it is installed but don't want it to be installed as part of your package and you don't want to reference it as part of the Imports or Suggests fields in a package DESCRIPTION.

Usage

.optional_fn(
  pkg,
  name,
  alt = function(...) {
     stop("function `", pkg, "::", name, "(...)` not available")

    }
)

Arguments

pkg

the package name

name

the function you wish to use

alt

a function that can be used instead

Value

the function you want if available or the alternative

Examples

fn = .optional_fn("openssl", "md5", digest::digest)
as.character(fn(as.raw(c(1,2,3))))
#> [1] "5289df737df57326fcdd22597afb1fac"