Support for the Ruby 2.4 series has ended. See here for reference.
self
Switch
that takes an argument, which does not begin with '-'.
Returns nil if argument is not present or begins with '-'.
# File optparse.rb, line 705 def parse(arg, argv, &error) if !(val = arg) and (argv.empty? or /\A-/ =~ (val = argv[0])) return nil, block, nil end opt = (val = parse_arg(val, &error))[1] val = conv_arg(*val) if opt and !arg argv.shift else val[0] = nil end val end