1  function(check_string_option_value option)
 2    get_property(expected_values CACHE ${option} PROPERTY STRINGS)
 3    if(expected_values)
 4      if(${option} IN_LIST expected_values)
 5        return()
 6      endif()
 7      message(FATAL_ERROR "${option} value is \"${${option}}\", but must be one of ${expected_values}.")
 8    endif()
 9    message(AUTHOR_WARNING "The STRINGS property must be set before invoking `check_string_option_value' function.")
10  endfunction()