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#' A missing key object
#'
#' A \code{key_missing} object represents a missing key.
#'
#' @param x An object to test.
#'
#' @export
key_missing <- function() {
# Note: this is more verbose, but much faster than
# structure(list(), class = "key_missing")
x <- list()
class(x) <- "key_missing"
x
}
#' @rdname key_missing
#' @export
is.key_missing <- function(x) {
inherits(x, "key_missing")
}
#' @export
print.key_missing <- function(x, ...) {
cat("<Key Missing>\n")
}
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