[CMake] library name from subdirectory and setting the CACHE - a "listening" variable?

[Clifford Yapp]

Ironically, I now see this issue (almost exactly) was discussed long ago:

http://www.cmake.org/pipermail/cmake/2005-September/007204.html

However, when I try:

get_directory_property(PNG_LIB_NAME DIRECTORY src/other/libpng
DEFINITION PNG_LIB_NAME)
MESSAGE("getdirprop: ${PNG_LIB_NAME}")

I get nothing - anybody have a worked example using this feature?

Cheers, and sorry for the week Google skills,
CY