return quoted arguments of given expression

quoted_args.R

# Based on this stackoverflow answer (https://stackoverflow.com/a/57709169)
# from Valeri Voev

#' Return quoted arguments of given expression
#'
#' @param args Expression such  `x`, `"x"`, `c(x, y)` or `c("x", "y")`.
#'
#' @return The quoted arguments.
#'
#' @examples
#' return_args(x)
#' return_args("x")
#' return_args(c(x, y))
#' return_args(c("x", "y"))
#'
#' @noRd
return_args <- function(args) {
  args_expr <- enexpr(args)
  if(length(args_expr) == 1) {
    args_vars <- as.list(args_expr)
  } else {
    args_vars <- as.list(args_expr)[-1]
  }
  vapply(args_vars, quo_name, character(1))
}


#' Return names of arguments of given expression
#'
#' @param args Expression such  `c(a = x, b = y)` or `c(x, y)`.
#'
#' @return The arguments names if they exist.
#'
#' @examples
#' return_args(c(a = x, b = y))
#' return_args(c(a = x, y))
#' @noRd
return_args_names <- function(args) {
  expr <- rlang::enexpr(args)
  names(return_args(!!expr))
}


# Example use 1 
myfun <- function(counts) {
  counts <- rlang::enquo(counts)
  expr <- rlang::quo_get_expr(counts)
  arg_v <- return_args(!!expr)
  arg_n <- return_args_names(!!expr)
  if (!is.null(arg_v)) {
    cat("Argument values:\n")
    print(arg_v)
  }
  if (!is.null(arg_n)) {
    cat("Argument names:\n")
    print(arg_n)
  }
}


# Example use 2
myfun2 <- function(counts) {
  counts <- rlang::enquo(counts)
  expr <- rlang::quo_get_expr(counts)
  arg_v <- return_args(!!expr)
  arg_n <- names(arg_v)
  if (!is.null(arg_v)) {
    cat("Argument values:\n")
    print(arg_v)
  }
  if (!is.null(arg_n)) {
    cat("Argument names:\n")
    print(arg_n)
  }
}

myfun(x)
myfun("x")
myfun(c(nm1 = x, nm2 = y))
myfun(c(nm1 = x, y))

myfun2(x)
myfun2("x")
myfun2(c(nm1 = x, nm2 = y))
myfun2(c(nm1 = x, y))