[gcasa]

NeXTSTEP? That's how it started, but not where it currently is. GNUstep is currently pushing for 10.15 compatibility at least. GNUstep supports the current release of clang which is fully ObjC2 compliant. GCC is also still supported. There is also a tool called buildtool and a library which can read and build xcodeproj files fairly seamlessly.

[pjmlp]

Objective-C moved on, nowadays is it more 2.x than 2.0, and those small changes are not there as far as I am aware.

[gcasa]

Which small changes are you referring to? We use LLVM/clang and so does Apple. We have ARC, we have properties and other features as well. Be explicit... BTW, I'm the lead maintainer, so I kind of know what is there and what isn't.

[pjmlp]

Apple uses their own fork of LLVM/clang, hence why watchOS bitcode is more stable than what the open source variant offers.

"Swift and Objective-C Interoperability" - WWDC 2015 (Nullability qualifiers, audited regions, generics, typed collections, kind of types)

https://developer.apple.com/videos/play/wwdc2015/401/

"What's New in LLVM" - WWDC 2017 (API Availability checks, ARC warnings and stronger function declarations)

https://developer.apple.com/videos/play/wwdc2017/411/

"What's New in LLVM" - WWDC 2018 (ARC updates)

https://developer.apple.com/videos/play/wwdc2018/409/

"What's New in Clang and LLVM" - WWDC 2019 (runtime optimizations)

https://developer.apple.com/videos/play/wwdc2019/409/

"Advancements in the Objective-C runtime" - WWDC 2020

https://developer.apple.com/videos/play/wwdc2020/10163/

I didn't fell to go all the way back to the WWDC 2006 when Objective-C 2.0 was announced.

Explicit enough?