I have decompiled AppKit on macOS occasionally to debug issues in my app. For example, in one case I discovered that double clicking a cell sometimes only sele

I have decompiled AppKit on macOS occasionally to debug issues in my app. For example, in one case I discovered that double clicking a cell sometimes only selected part of the contents. With Hopper I was able to verify that the bug is that AppKit just selected the range from 0 to 32000, assuming that would be enough. I was able to work around the issue by manually selecting a bigger range. (I also reported the bug to Apple, they told me they won't fix it because it's a deprecated API. Doesn't matter that 100s of apps, including Apple's own, were still using it...) In another case, I found out that an obscure feature (text attachments with custom cells) was crashing because AppKit called -release too often, so it was impossible to use the feature. Apple had apparently broken it when implementing the force touch functionality for dictionary lookups. Another time Cornerstone, the SVN client, was broken on a prerelease version of macOS. I don't recall the details, I think they called -registerDefaults: too early. I was able to fix it by writing a dynamic library that changed the -registerDefaults: implementation so that it ignored the first call (today with hardened runtime this fix wouldn't be possible anymore without disabling system integrity protection).