[CMake] Using variable to store variable name

[Paul Smyth]

Hi folks,
This seems to me like a dumb question; but I can't seem to find the
answer, in all my searching.

You can build a variable name from a the value of another variable. And
then extract the value pointed to my the built variable name.
Like so: (taken from UseSWIG.cmake)
${SWIG_MODULE_${name}_REAL_NAME}

However, in the simpler case, if you have a variable A whose contents
are another variable name B, the you don't seem to be able to extract
the value of variable B.
e.g.

SET(B "BVALUE")
SET(A "B")

WRITE_FILE("C:\\Temp\\Libs.txt" "A = <${A}>" APPEND )
WRITE_FILE("C:\\Temp\\Libs.txt" "B = <${B}>" APPEND )
WRITE_FILE("C:\\Temp\\Libs.txt" "B's value from A = <${${A}}>" APPEND )

This results in 
AVAR = <BVAR>
BVAR = <BVALUE>
BVAR's value from AVAR = <}>

Which is obviously not right.

Am I realistic in expecting this to work?
Why does it seem to work in the case of aggregating names, but not more
directly?
Is there a workaround or fix about?
If it should work, then I might look a bit harder at the parsing code,
but it's a bit yucky.

Thanks for any help you can give,
Paul Smyth

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