Do string mixins work under -betterC?

[DLearner]

I have a rather complicated string mixin defined and invoked from 
within the same source file.
Which seems to work.

But when I move the mixin definition to a separate module, and 
import that module into the original source file, the compilation 
collapses complaining that array concatenation requires the GC, 
which is not available with -betterC.

DLearner