Error: ambiguity found when searching for best transformation
Trying to produce type 'OBJ' from:
 -  { auto_diff.c.C }
Generators that succeeded:
 -  darwin.compile.c++
 -  darwin.compile.c
First generator produced:
 -  { darwin%darwin.compile.c++-auto_diff.o.OBJ { swig%swig.generate-code-auto_diff.cpp.CPP { darwin%darwin.compile.c.preprocess-auto_diff.i.PREPROCESSED_C { auto_diff.c.C } } } }

Second generator produced:
 -  { darwin%darwin.compile.c-auto_diff.o.OBJ { auto_diff.c.C } }