use of -flat_namespace on darwin

[Adam Mercer]

Hi

In one of our projects we are experiencing a problem which seems to be
related to the fact that the -flat_namespace option is not being
passed to the linker, looking into why this is the case I see the
following code in libtool.m4:

    case $host_os in
    rhapsody* | darwin1.[[012]])
      _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
    darwin1.*)
      _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined
${wl}suppress' ;;
    darwin*) # darwin 5.x on
      # if running on 10.5 or later, the deployment target defaults
      # to the OS version, if on x86, and 10.4, the deployment
      # target defaults to 10.4. Don't you love it?
      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
        10.0,*86*-darwin8*|10.0,*-darwin[[91]]*)
          _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
        10.[[012]]*)
          _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined
${wl}suppress' ;;
        10.*)
          _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
      esac
    ;;
  esac

I see that the -flat_namespace is only passed for 10.0, 10.1, and
10.2. Why is this? Are there adverse effects to using a flat namespace
on more recent OS X versions?

Cheers

Adam