Comment 1 for bug 1597594

Trying to do a bit of sleuthing on this.
I note that when I run cmake I get the message along the lines (I didn't get a copy) "optional not found falling back to Boost"

If I look at file 'FindOptional.cmake', I see...

IF (OPTONAL_INCLUDE_DIR)
  # Already in cache, be silent
  SET(OPTOINAL_FIND_QUIETLY TRUE)
ENDIF()

FIND_PATH(OPTIONAL_INCLUDE_DIR optional.hpp
  /usr/local/include
  /usr/include
  ${SOURCE_BASE_DIR}/Optional-master
)

include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(Optional DEFAULT_MSG
                                  OPTIONAL_INCLUDE_DIR)

MARK_AS_ADVANCED(
  OPTIONAL_INCLUDE_DIR
)

Looks like a few tripewirting errors in this, but maybe of no consequence anyway.

Cheers,
Terry