[RandallBrown]

So the previous code wouldn't compile unless the compiler knew what values were going to be passed into whatDoesItReturn?

[lumberjackstian]

Aye correct! I should've been more clear about that, sorry.

Template arguments need to be known at compile time, and the extra set of parens is how templates parameters are declared in D.

[DougBTX]

I missed this the first time, but there are two sets of parentheses in the example. Apparently the first set are like template parameters, and the second are the actual arguments to the function.