Why doesn't this have a length?

[Magnus Lie Hetland]

In a template class (with State and Input as template parameters), I 
have the following (private) member:

State[][Tuple!(const(State), const(Input))] transitions;

It works well enough, but for some reason I can't access its length 
attribute...? (If I define other simpler, similar private attributes, 
such as uint[uint], I can access their length in the same location 
where transition.length fails.)

I get an error message that seems to indicate that DMD is looking for a 
global identifier. I've tried instantiating with different types, e.g., 
uint.

Am I doing something illegal?-)

-- 
Magnus Lie Hetland
http://hetland.org