#' Determine if/which vector element are options flags
#'
#' Determines if an element of a vector is an option flag (as opposed to a
#' value ) by checking against the option style
#'
#' @details `is_flag` and `which.flag` are internal functions not
#' expected to be called directly.
#'
#' They are used to identify which elements of the option vector are
#' option names (as opposed to option values). Options are identified by
#' `getOptions('optigrab')$style$flag_test`. By defailt, **optigrab**
#' follows GNU-style command line arguments, i.e. those beginning with
#' "--" or "-" and are set at the time of package loading.
#'
#' @param x vector of options, for example `commandArgs()`.
#' @return logical. indicating which arguments are flags.
#' @examples
#' optigrab:::is_flag( c( "--foo", "bar") )
#' optigrab:::is_flag( c( "--foo", "bar", "-f", "-b", "text" ) )
#'
is_flag <- function(x) {
return( getOption("optigrab")$style$flag_test(x) )
}
is.flag <- function(...) {
.Deprecated("is_flag", old="is.flag")
is_flag(...)
}
#' @rdname is_flag
#' @return numeric
#' @examples
#' optigrab:::which.flag( c( "--foo", "bar") )
#' optigrab:::which.flag( c( "--foo", "bar", "-f", "-b", "text" ))
#'
which.flag <-function(x) which( is_flag(x) )
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