Separation of Concerns by using policy-based design.cpp

template <bool retainAutorelease>
static ALWAYS_INLINE id Kotlin_ObjCExport_refToObjCImpl(ObjHeader* obj) {
  if (obj == nullptr) return nullptr;

  if (obj->has_meta_object()) {
    id associatedObject = GetAssociatedObject(obj);
    if (associatedObject != nullptr) {
      return retainAutorelease ? objc_retainAutoreleaseReturnValue(associatedObject) : associatedObject;
    }
  }

  // TODO: propagate [retainAutorelease] to the code below.

  convertReferenceToObjC converter = (convertReferenceToObjC)obj->type_info()->writableInfo_->objCExport.convert;
  if (converter != nullptr) {
    return converter(obj);
  }

  return Kotlin_ObjCExport_refToObjC_slowpath(obj);
}
/**
Здесь нехорошо то, что функция `Kotlin_ObjCExport_refToObjCImpl` смешивает две проблемных области (domains):
1. Business domain: create and store (slow path) or fetch (fast path) the associated object
2. ARC domain: retain policy

Try orthogonal design by Separation of Concerns: separate policy from business code:
*/
template <typename RetainAutoreleasePolicy>
static ALWAYS_INLINE id Kotlin_ObjCExport_refToObjCImpl(ObjHeader* obj) {
  if (obj == nullptr) return nullptr;
  
  if (obj->has_meta_object()) {
    if (id associatedObject = GetAssociatedObject(obj)) {
        return RetainAutoreleasePolicy(associatedObject);
    }
  }
// ... no changes below...
}

/// Usage example:

std::function<id (id)> doRetain = [](id obj) { return objc_retainAutoreleaseReturnValue(obj); };
std::function<id (id)> doNotRetain = [](id obj) { return obj; };

id foo = Kotlin_ObjCExport_refToObjCImpl<doRetain>(obj);