$ cat host.d

import std.exception;
import core.runtime;
import core.sys.posix.dlfcn;
import common;

void main(string[] args)
{
	auto lib = Runtime.loadLibrary(args[1]).enforce("Failed to load library");
	auto getter = cast(Getter*)dlsym(lib, "getInstance").enforce("Failed to get `getInstance`");
	auto instance = (*getter)();
	instance.foo();
}

$ cat a.d
import common;
class Baz : Bar
{
	override void foo()
	{
		import std.stdio;
		writeln("It works!");
	}
}

extern(C) Bar getInstance() { return new Baz; }

$ cat common.d 
interface Bar
{
	void foo();
}

extern(C) Bar getInstanceDL();
alias Getter = typeof(getInstanceDL);

$ cat build.sh
# NOTE: you must create a symlink the shared version of Phobos or update the
# rpath references appropriately
DC="dmd"

# Host
$DC -g host.d common.d -L-ldl -map -defaultlib=libphobos2.so -L-rpath=.

# a.so
$DC -c a.d -fPIC -ofa.o common.d
$DC -ofa.so a.o -shared -defaultlib=libphobos2.so -L-rpath=.

$./build.sh
$./host "$PWD/a.so"
Fatal Error while loading '/home/justin/workspace/aiasflow/tests/interfaces/a.so':
	The module 'common' is already defined in './host'.
Segmentation fault