C<subtract_off>. Then one can use
#define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \
- ((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32])
+ ((XSINTERFACE_CVT_ANON(ret))fp[CvXSUBANY(cv).any_i32])
#define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \
CvXSUBANY(cv).any_i32 = CAT2( f, _off )