Undefined symbol ModuleInfoZ when including a SWIG generated module

[Walter Gray via Digitalmars-d-learn]

Hi there,
  I'm currently trying to set up a small demo project using the 
Leap Motion API in D.  I've run SWIG with -d -d2, and created the 
intermediate C++ DLL along with a pair of .d files, leap.d and 
leap_im.d.  I'm new to D, but very interested and I'd like to set 
this up in an idiomatic way & be able to share it, but I'm 
running into a problem: When I create a simple sample project 
with Visual D and import the Leap module, I get a number of 
linker errors:

Error 42: Symbol Undefined 
_D4Leap10Controller6__ctorMFZC4Leap10Controller (Leap.Controller 
Leap.Controller.__ctor())
Error 42: Symbol Undefined _D4Leap10Controller7__ClassZ
Error 42: Symbol Undefined _D4Leap12__ModuleInfoZ

I've discovered that if I run dmd manually and link in the object 
files for leap.d and leap_im.d, these problems go away, and if I 
create a separate project to build a .lib and then link to that 
it also solves the issue.  Both of these options seem hacky to me 
though, and I'm wondering if there's some 3rd option I'm missing 
- the files contain the entire definitions, so why would it be 
necessary to link to them AND specify them as imports?  What am I 
missing here?