Many, though I have to start with this disclaimer: I still don't fully understand why Objective-C is such a sweet spot.
One very important one is that, empirically, it showed how much of what we think we know about language design is ... shall we say ... "incomplete".
After all, Objective-C is a car-crash of a language: take some Smalltalk and jam it into C. Done. How can you write software with this? And yet NeXTStep and Cocoa/CocoaTouch, arguably the most elegant pieces of OS-level/UI-framework software ever, were written in Objective-C. And not despite of it, but because of it.
From a safety standpoint, it's hard to see how you can get worse: all the static type safety of Smalltalk (none) combined with the memory safety of C (none). And these interact.
And while it certainly is possible to use it very, very badly, in practice I haven't seen the horrors that we are supposed to get.
As an example, we got the same level of improvement from doing an Objective-C → Objective-C rewrite with Wunderlist (from WL2 to WL3) that others claim for Objective-C to Swift transitions.
Also, dynamic messaging is said to be slow, yet Objective-C programs consistently outperform the much more static Swift ones.
And of course, we all know that to do dynamic OO, you need a large runtime and better yet a VM. But it turns out that you can get much if not all of it with a tiny sliver of an extension to portable PDP-11 assembly language.
One very important one is that, empirically, it showed how much of what we think we know about language design is ... shall we say ... "incomplete".
After all, Objective-C is a car-crash of a language: take some Smalltalk and jam it into C. Done. How can you write software with this? And yet NeXTStep and Cocoa/CocoaTouch, arguably the most elegant pieces of OS-level/UI-framework software ever, were written in Objective-C. And not despite of it, but because of it.
From a safety standpoint, it's hard to see how you can get worse: all the static type safety of Smalltalk (none) combined with the memory safety of C (none). And these interact.
And while it certainly is possible to use it very, very badly, in practice I haven't seen the horrors that we are supposed to get.
https://blog.metaobject.com/2014/05/the-spidy-subset-or-avoi...
As an example, we got the same level of improvement from doing an Objective-C → Objective-C rewrite with Wunderlist (from WL2 to WL3) that others claim for Objective-C to Swift transitions.
Also, dynamic messaging is said to be slow, yet Objective-C programs consistently outperform the much more static Swift ones.
https://www.amazon.com/gp/product/0321842847/ref=as_li_tl?ie...
And of course, we all know that to do dynamic OO, you need a large runtime and better yet a VM. But it turns out that you can get much if not all of it with a tiny sliver of an extension to portable PDP-11 assembly language.
https://blog.metaobject.com/2024/08/objective-c-is-just-like...
With so much being provided by so little, you can actually put the rest of the language design space to better use, IMHO:
https://objective.st