[swift-dev] Swift root meta-class

[Giacomo Leopizzi]

Yes, of course. It’s just the will to understand more low level stuffs about Swift. We downloaded the file and what we understand is that the root-class is always SwiftObject but if SWIFT_OBJC_INTEROP is defined it create the necessary “bridges” for working with ObjC. Many thanks for the kind answer, we go to bed because here is almost 2 o’clock am and tomorrow we have to go to the Apple Developer Academy.

Kind regards,
Giacomo and Annino 

> On 9 May 2017, at 01:00, John McCall <rjmccall at apple.com> wrote:
> 
>> On May 8, 2017, at 6:46 PM, Giacomo Leopizzi <gi.le at icloud.com> wrote:
>> Our starting point was that in ObjC at the beginning of the execution, the root meta-class (most of the time NSObject) instantiates all the other meta-classes, that create the class as object for the software.
> 
> This is somewhat like how a Smalltalk VM is bootstrapped, but there isn't any real sense in which root classes control how classes are created or loaded in ObjC.
> 
>> In Swift is it the same? If so, which is the name of the root meta-class? 
> 
> The root class of a Swift class is a private implementation detail; it's not guaranteed in any way.
> 
> If you're just curious about the current implementation, you can look in stdlib/public/runtime/SwiftObject.mm, but again, nothing in there is something that you should rely on as a Swift programmer.
> 
> John.
> 
>> Thanks for the fast reply. 
>> 
>> Giacomo 
>> 
>>> On 9 May 2017, at 00:30, John McCall <rjmccall at apple.com> wrote:
>>> 
>>>> On May 8, 2017, at 6:21 PM, Giacomo Leopizzi via swift-dev <swift-dev at swift.org> wrote:
>>>> Hello everyone! 
>>>> I was discussing with a friend about metaclasses in Objective-C. In Obj-C the root meta-class was the NSObject's one.
>>> 
>>> ObjC does not have a single root class.  Most ObjC classes inherit from NSObject, but that is not guaranteed, and in fact there are other common root classes including NSProxy.
>>> 
>>>> When in a swift class you create a subclass of NSObject, the root metaclass should be the same. What happen when you delcare a class without NSObject dependence? There is an hidden root-class? Where can we read more about this topic? 
>>> 
>>> When ObjC interop is enabled, Swift classes that do not inherit from NSObject use a private root class.  However, that is a private implementation detail and we don't promise much about it.
>>> 
>>> Do you have any specific questions?
>> 
>>> 
>>> John.
>> 
>