Seems to crash when trying to get the type of a UIViewController.

[valleyman86]

The following code will crash

class ViewController: UIViewController { }
let info = try? typeInfo(of: ViewController.self)

in
RelativePointer->advanced()
on
let offsetCopy = self.offset

Any ideas what would cause this?

[wickwirew]

What version of swift?

[valleyman86]

Swift 4.2

[valleyman86]

Not sure if it is relevant but let info = try? typeInfo(of: UIViewController.self) will return nil. The error being "couldNotGetTypeInfo". I assume this is because "Runtime.Kind.objCClassWrapper" is not supported.

[valleyman86]

Update: I was able to get objC classes to work by adding support for an ObjCWrapper. I am now able to createInstance on things like UIViewController and UIButtons.

As for this crash I think it is related to accessing typeDescriptor (Nominal Type Descriptor). From what I understand in swift 4.2 this is going away right? Anyways I didn't see Runtime doing much with mangledName so I commented that out (I dont need it for my use case anyways). I then set the properties for the class using ObjC runtime if the rodataPointer lowest bit is 0. According to the docs this will be 1 for swift classes and it seemed to reflect that in my testing.

Long story short I think I got this mostly working now. Maybe I can make a PR for this later but I was honestly unable to get SPM working and cocoapods was out of date so I just manually created a new framework for runtime.

[valleyman86]

Seems after getting an object created and such I still cant set the values of a swift class that inherits from UIViewController. (Same code as above). No error it just doesn't do anything and the values remain whatever they were. I suspect this is an issue with a class that inherits from NSObject eventually cant have its values set the same way... not quite sure.

[valleyman86]

Further research into this suggest it may because we need to account for the super class when dealing with the field offsets. I was able to detect that the first field is actually perfectly offset at the value returned by class_getInstanceSize of the superclass.

I found this code in the swift runtime (Metadata.h)

unsigned getFieldOffsetVectorOffset(const ClassMetadata *metadata) const {
    const auto *description = metadata->getDescription();

    if (description->hasResilientSuperclass())
      return metadata->Superclass->getSizeInWords() + FieldOffsetVectorOffset;

    return FieldOffsetVectorOffset;
  }

I guess the main challenge here is that these fields are only used for swift objects.

[wildthink]

@valleyman86
How did you fix the support for ObjCWrapper.?
#36 (comment)
thanks.

[NSExceptional]

@wickwirew any update on this? I'm running into very simple issues when working with objects, wondering if this is related.

Edit: opened a new issue about this #81