usage of ref foreach with variadic functions fails with "cannot be ref"

[error via Digitalmars-d-learn]

I'm making a serializer that has a variadic write method that 
takes arbitrary params
and serializes them;  I want to do the same thing with a read 
method ( pass in your
params by ref, and it populates them with data ) -  however, I 
run into a compiler
error - "cannot be ref" in the foreach statement...  Anyone know 
a workaround for this?  Is this a bug, or by design?

Simplified example:

void populateVars(T...)(T vars){
   // Generates "cannot be ref" compiler error:
   foreach(ref v; vars){
     // Populate v with some data here...
   }
}