This project is a Swift interface for GNUStep's version of AppKit.

This project assumes that you are running OnFlapp's GNUStep Desktop project. To build, you need to install GNUStep Desktop [https://onflapp.github.io/gs-desktop/index.html] on Debian, then install Swift version 5.8.1 on Debian.

IMPORTANT: This assumes that file system layout of Onflapp's GNUstep Desktop environment.

GORM File and Info_gnustep.plist

I haven't yet figured out how to configure Swift to copy the files into the a folder called Resources within the same folder holds the built Swift executable. For now, just copy in the Resources folder into the .build/build/debug folder.

NSObject Integration

AppKit is a Swif tlibrary that wraps GNUStep's gui library. HelloWorld is my playground. It is often not working. NSWindowTest is to strictly test the code that creates NSWindow. It runs well!

class GNUStepNSObjectWrapper

This is a class written in Swfit that is responsible to instantiate GNUStep ObjC classes. When it instantiates a new NSObject, it always calls retain. If it is just wrapping a alreday made pointer, currently it does not call retain.

If you intend to wrap a new subclass of an existing NSObject, Objective-C object, then you need to implement GNUStepNSObjectSubclassConstructor first, then you can wrap that subclass.

class GNUStepNSObjectSubclassConstructor

This class is responsible for adding new objects to the GNUStep ObjC runtime. Every new object that it creates gets an additional Ivar called ___swiftPtr that hols a pointer to the Swift object that it wraps.

retain and release

Currently, I have a class called GNUStepNSObjectWrapper that holds a reference to a NSObject in the GNUStep ObjC runtime. This object retains any NSObjects that is creates. However, we may get that same object back in the form of an id from the GNUStep ObjC2 runtime via a call to objc_msgSend or smart_swift_lookupIvar.

When we recieve that object we either have to (a) construct a new wrapper calss. This is easy, we can just call object_getClassName() and use the retrieved name to map it to a Swift class that will wrap that id or (b) we can take the id value and look up a Swift object that was already instantiated and wraps it.

Question 1: How do we manage retains?

Question 2 What is the best way to store a table of the objects?

Calling Objective-C Methods From Swift

One of the major issues that I faced was getting objc_msgSend and objc_msgSend_stret to play nicely with swift. Each of these functions are used to send messages (call methods) of an Objective-C object. Unfortunatley, I never got that working right, instead, I implemented a funciton objc_smart_getIMP which calls class_getMethodImplementation. The term 'smart' here just means that I am making the function swiftier, and it helps do lookup and casting for me. There are two version of this function

public func objc_smart_getIMP<T>(object: GNUStepNSObjectWrapper, selector: String) -> T? {
	let c = object_getClass(&object._nsobjptr!.pointee)
	let v = class_getMethodImplementation(c, sel_getUid(selector))
	let rt: T? = unsafeBitCast(v, to: T.self)
	return rt
}

public func objc_smart_getIMP<T>(id: GNUStepNSObjectPointer, selector: String) -> T? {
	var id = id
	let c = object_getClass(id)
	let v = class_getMethodImplementation(c, sel_getUid(selector))
	let rt: T? = unsafeBitCast(v, to: T.self)
	return rt
}

Pure Swift Objects Corssing Into Objective-C (NSSwiftObjectWrapper?)

Classes like NSArray and NSDictionary suffer from only being able to store NSObjects. It may be nice to be able to put Swift objects into these arrays. We would need to wrap them into something in order to do this.

An NSSwiftObject wrapper type could be introduced which can hold a pointer back to the original Swift object; however, would need to manage retaining any Swift reference types. Some ideas are presented here. In this blog that may help us construct this. It would be nice if this was a part of the GNUStep's Foundation.

https://theswiftdev.com/how-to-use-a-swift-library-in-c/

THE FOLLOWING IS MOSTLY SOLVED (SEE ABOVE)

objc_msgSend and objc_msgSend_stret

objc_msgSend() is a c function used by the Objective-C runtime to send messages. Unfortunately it has a variable arguments which cannot be imported into Swift. To overcome this, I have created some specialized versions of of objc_msgSend that have different number of arguments. These can be found in the ObjCSwiftInterop.c file.

Ultimately, I would like a swift version of this which more intelligently decides how to map the values. I started work on this, in the AppKit.swift file called func objc_smart_sendMessage<T>(object: NSObjectGNUStepSwiftBridge, selector: String, value1: Any?, value2: Any?, value3: Any?, value4: Any?, value5: Any?, value6: Any?, value7: Any?, value8: Any?, value9: Any?) -> T?

This solves the problem that we have to send messages of arbitrary side, but it does not solve the issues around casting, and that two separate functions objc_msgSend and objc_msgSend_stret depending on which type we are going to get back from.

CASTING

Just some thoughts and notes: Please correct me where I am wrong or misunderstanding.

objc_msgSend and objc_msgSend_stret are very difficult functions to properly import into Swift. objc_msgSend is used for messages that return Objective-C classes, and simple data values that have the same size as id . From what I understand, both require the the function to be properly cast to work and because they are implemented in assembly and they are doing some magic with the registers to properly get the result. objc_msgSend returns void* but objc_msgSend_stret on GNUStep's runtime returns void. Before you can use objc_msgSend_stret, you have to cast it to a function that returns the value you are expecting.

UIView *view = [[NSView alloc] initWithFrame:NSRectZero];

NSRect (*sendRectFn)(id receiver, SEL operation);
sendRectFn = (NSRect(*)(id, SEL))objc_msgSend_stret;
NSRect frame = sendRectFn(view, @selector(frame));

Idea 1: THIS DOES NOT WORK. I really have no idea what I am doing. LOL

void* forSwift_objcMsgSend_stret(id ID, SEL cmd, int64_t returnSize) {
	printf("forSwift_objcMsgSend_stret\n");
	void* itemArr = malloc(returnSize);
	void* (*sendRectFn)(id receiver, SEL operation);
	sendRectFn = (void(*)(id, SEL))objc_msgSend_stret;
	itemArr = sendRectFn(ID, cmd);
	return itemArr;
}

**Inspiration: 1 ** This stackoverflow post suggests using class_getMethodImplementation_stret. https://stackoverflow.com/questions/54002375/swift-runtime-calling-superclass-method

What we need to be able to do is express this in Swift using

I do not know how the objc_msgSend_stret knows what the returned data type should be.