[CMake] what is wrong with this snippet? (bug?)

[Matthew Woehlke]

set(!BANG wacky CACHE STRING "" FORCE)
set("var with space" wacky CACHE STRING "" FORCE)
message(STATUS "This is !BANG: ${!BANG}")
message(STATUS "This is var with space: ${var with space}")

The above snippet (as expected) causes a CMake error. What's interesting 
is that the error is in the message, not the set. More so, the variables 
do indeed end up in the cache!

The utility of a variable that can't be referenced seems... dubious. 
Should CMake prevent this?

(cmake 2.6-2)

-- 
Matthew
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-- 
C++ is for people who want to be able to not just shoot themselves in 
the foot, but do it with a rocket launcher. -- Igor Peshansky