(cffi:defcenum option-arg
  :none
  :string
  :int
  :callback
  :filename
  :string-array
  :filename-array
  :double
  :int64)  

:none

No extra argument. This is useful for simple flags.

:string

The option takes a string argument.

:int

The option takes an integer argument.

:callback

The option provides a callback function to parse the extra argument.

:filename

The option takes a filename as argument.

:string-array

The option takes a string argument, multiple uses of the option are collected into a list of strings.

:filename-array

The option takes a filename as argument, multiple uses of the option are collected into a list of filenames.

:double

The option takes a double float argument. The argument can be formatted either for the locale of the user or for the C locale.

:int64

The option takes a 64-bit integer. Like the :int value but for larger numbers.