結局こういう感じになりました：
bool solve(..., LBVectorComponent **xcomps, size_t *xcomps_cnt);
var xcomps_ptr: UnsafeMutablePointer<LBVectorComponent>? = nil var xcomps_c = 0 if LinBoxWrapper.solve(..., &xcomps_ptr, &xcomps_c) { guard let xcomps_ptr = xcomps_ptr else { fatalError() } let buff = UnsafeBufferPointer(start: xcomps_ptr, count: xcomps_c) defer { xcomps_ptr.deallocate() } return DVector(size: size.cols, components: buff) } else { ... (edited)