C++ CanType::isExactSuperclassOf方法代码示例

/// Given two class types, check whether there's a hierarchy relationship
/// between them.
static DynamicCastFeasibility
classifyClassHierarchyCast(CanType source, CanType target) {
  // Upcast: if the target type statically matches a type in the
  // source type's hierarchy, this is a static upcast and the cast
  // will always succeed.
  if (target->isExactSuperclassOf(source))
    return DynamicCastFeasibility::WillSucceed;

  // Upcast: if the target type might dynamically match a type in the
  // source type's hierarchy, this might be an upcast, in which
  // case the cast might succeed.
  if (target->isBindableToSuperclassOf(source))
    return DynamicCastFeasibility::MaySucceed;

  // Downcast: if the source type might dynamically match a type in the
  // target type's hierarchy, this might be a downcast, in which case
  // the cast might succeed.  Note that this also covers the case where
  // the source type statically matches a type in the target type's
  // hierarchy; since it's a downcast, the cast still at best might succeed.
  if (source->isBindableToSuperclassOf(target))
    return DynamicCastFeasibility::MaySucceed;

  // Otherwise, the classes are unrelated and the cast will fail (at least
  // on these grounds).
  return DynamicCastFeasibility::WillFail;
}

/// Can the given cast be performed by the scalar checked-cast
/// instructions?
bool swift::canUseScalarCheckedCastInstructions(SILModule &M,
                                                CanType sourceType,
                                                CanType targetType) {
  // Look through one level of optionality on the source.
  auto objectType = sourceType;
  if (auto type = objectType.getOptionalObjectType())
    objectType = type;

  // Casting to NSError needs to go through the indirect-cast case,
  // since it may conform to Error and require Error-to-NSError
  // bridging, unless we can statically see that the source type inherits
  // NSError.
  
  // A class-constrained archetype may be bound to NSError, unless it has a
  // non-NSError superclass constraint. Casts to archetypes thus must always be
  // indirect.
  if (auto archetype = targetType->getAs<ArchetypeType>()) {
    // Only ever permit this if the source type is a reference type.
    if (!objectType.isAnyClassReferenceType())
      return false;
    
      auto super = archetype->getSuperclass();
      if (super.isNull())
        return false;

    // A base class constraint that isn't NSError rules out the archetype being
    // bound to NSError.
    if (M.getASTContext().LangOpts.EnableObjCInterop) {
      if (auto nserror = M.Types.getNSErrorType())
         return !super->isEqual(nserror);
    }
    
    // If NSError wasn't loaded, any base class constraint must not be NSError.
    return true;
  }
  
  if (M.getASTContext().LangOpts.EnableObjCInterop
      && targetType == M.Types.getNSErrorType()) {
    // If we statically know the source is an NSError subclass, then the cast
    // can go through the scalar path (and it's trivially true so can be
    // killed).
    return targetType->isExactSuperclassOf(objectType);
  }
  
  // Three supported cases:
  // - metatype to metatype
  // - metatype to object
  // - object to object
  if ((objectType.isAnyClassReferenceType() || isa<AnyMetatypeType>(objectType))
      && targetType.isAnyClassReferenceType())
    return true;

  if (isa<AnyMetatypeType>(objectType) && isa<AnyMetatypeType>(targetType))
    return true;
  
  // Otherwise, we need to use the general indirect-cast functions.
  return false;
}

//.........这里部分代码省略.........
  if (sourceClass) {
    if (targetClass) {
      // Imported Objective-C generics don't check the generic parameters, which
      // are lost at runtime.
      if (sourceClass->usesObjCGenericsModel()) {
      
        if (sourceClass == targetClass)
          return DynamicCastFeasibility::WillSucceed;
        
        if (targetClass->usesObjCGenericsModel()) {
          // If both classes are ObjC generics, the cast may succeed if the
          // classes are related, irrespective of their generic parameters.
          auto isDeclSuperclass = [&](ClassDecl *proposedSuper,
                                      ClassDecl *proposedSub) -> bool {
            do {
              if (proposedSuper == proposedSub)
                return true;
            } while ((proposedSub = proposedSub->getSuperclassDecl()));
            
            return false;
          };
          
          if (isDeclSuperclass(sourceClass, targetClass))
            return DynamicCastFeasibility::MaySucceed;
          
          if (isDeclSuperclass(targetClass, sourceClass)) {
            return DynamicCastFeasibility::WillSucceed;
          }          
          return DynamicCastFeasibility::WillFail;
        }
      }


      if (target->isExactSuperclassOf(source, nullptr))
        return DynamicCastFeasibility::WillSucceed;
      if (target->isBindableToSuperclassOf(source, nullptr))
        return DynamicCastFeasibility::MaySucceed;
      if (source->isBindableToSuperclassOf(target, nullptr))
        return DynamicCastFeasibility::MaySucceed;

      // FIXME: bridged types, e.g. CF <-> NS (but not for metatypes).
      return DynamicCastFeasibility::WillFail;
    }

    // Casts from a class into a non-class can never succeed if the target must
    // be bridged to a SwiftValueBox. You would need an AnyObject source for
    // that.
    if (!target.isAnyExistentialType() &&
        !target.getClassOrBoundGenericClass() &&
        !isa<ArchetypeType>(target) &&
        mustBridgeToSwiftValueBox(M, target)) {
      assert((target.getEnumOrBoundGenericEnum() ||
              target.getStructOrBoundGenericStruct() ||
              isa<TupleType>(target) ||
              isa<SILFunctionType>(target) ||
              isa<FunctionType>(target) ||
              isa<MetatypeType>(target)) &&
             "Target should be an enum, struct, tuple, metatype or function type");
      return DynamicCastFeasibility::WillFail;
    }


    // In the Objective-C runtime, class metatypes are also class instances.
    // The cast may succeed if the target type can be inhabited by a class
    // metatype.
    // TODO: Narrow this to the sourceClass being exactly NSObject.

//.........这里部分代码省略.........
      // (noreturn isn't really reified at runtime though.)
      if (targetFunction->isNoReturn() && !sourceFunction->isNoReturn())
        return DynamicCastFeasibility::WillFail;
      
      // The cast can't change the representation at runtime.
      if (targetFunction->getRepresentation()
            != sourceFunction->getRepresentation())
        return DynamicCastFeasibility::WillFail;
      
      if (sourceFunction.getInput() == targetFunction.getInput()
          && sourceFunction.getResult() == targetFunction.getResult())
        return DynamicCastFeasibility::WillSucceed;

      auto isSubstitutable = [](CanType a, CanType b) -> bool {
        // FIXME: Unnecessarily conservative; should structurally check for
        // substitutability.
        return a == b || a->hasArchetype() || b->hasArchetype();
      };
    
      if (isSubstitutable(sourceFunction.getInput(), targetFunction.getInput())
          && isSubstitutable(targetFunction.getInput(),
                             targetFunction.getResult()))
        return DynamicCastFeasibility::MaySucceed;
      
      return DynamicCastFeasibility::WillFail;
    }
  }

  // Class casts.
  auto sourceClass = source.getClassOrBoundGenericClass();
  auto targetClass = target.getClassOrBoundGenericClass();
  if (sourceClass) {
    if (targetClass) {
      if (target->isExactSuperclassOf(source, nullptr))
        return DynamicCastFeasibility::WillSucceed;
      if (target->isBindableToSuperclassOf(source, nullptr))
        return DynamicCastFeasibility::MaySucceed;
      if (source->isBindableToSuperclassOf(target, nullptr))
        return DynamicCastFeasibility::MaySucceed;

      // FIXME: bridged types, e.g. CF <-> NS (but not for metatypes).
      return DynamicCastFeasibility::WillFail;
    }

    // In the Objective-C runtime, class metatypes are also class instances.
    // The cast may succeed if the target type can be inhabited by a class
    // metatype.
    // TODO: Narrow this to the sourceClass being exactly NSObject.
    if (M->getASTContext().LangOpts.EnableObjCInterop) {
      if (auto targetMeta = dyn_cast<MetatypeType>(target)) {
        if (isa<ArchetypeType>(targetMeta.getInstanceType())
            || targetMeta.getInstanceType()->mayHaveSuperclass())
          return DynamicCastFeasibility::MaySucceed;
      } else if (isa<ExistentialMetatypeType>(target)) {
        return DynamicCastFeasibility::MaySucceed;
      }
    }
  }

  // If the source is not existential, an archetype, or (under the ObjC runtime)
  // a class, and the destination is a metatype, there is no way the cast can
  // succeed.
  if (target->is<AnyMetatypeType>()) return DynamicCastFeasibility::WillFail;

  // FIXME: tuple conversions?