An iOS App in Assembly (2014) | Hacker News Reader

An iOS App in Assembly (2014)

github.com

111 pointsbenguild31 comments

Everyone that says "but it's insane to use assembly to write an iOS app!" is both 100% correct and 100% missing the point. It's nice to float around on the surface most of the time and ship useful code, but if you don't spend at least a little of your time digging deep you'll miss out on a lot.

I'd never try to do this in prod, and neither would OP, but it's great to see how it works under the hood.

what is more interesting is his other project to make an application in pure C: https://github.com/richardjrossiii/CBasediOSApp. When you are doing cross-platform, you may be more at ease with a few lines of C for some utilities call if you don't want to learn objective C.

Whoa that looks so much simpler to me than ObjC. Of course I'm being a little naive because I haven't looked for moment at what those headers contain or how the API works, but just the same—that C version looks clean.

I wonder what developing a more complex application would look like.

I don't think it looks "simpler" than ObjC. He's still making the ObjC method calls, but with even more verbosity. I'd abstract all that away into macros or function calls ... but then you're right back to ObjC.

He just de-sugared [foo bar] into objc_msgSend(foo, sel_getUid(“bar”))

And probably lost a ton of compiler assisted type checking in the process. I hope nobody considers doing anything remotely like this for any reason beyond learning a little about the low-level Objective-C machinery.

It’s definitely NOT cross-platform. He’s just calling the objective-c runtime from C.

Maybe I'm reading wrong, but I read it more that if the Objective-C interface is small, i.e. the bulk of your app is cross-platform C, you could easily use C to interact with the runtime.

So why not just write the Objective-C part in C rather than calling the underlying machinery directly. It's a neat project to learn the internals, but I wouldn't ever structure a real app this way.

If you write part of it in C, then you can reuse that code on another platform.

Objective-C is a superset of C though, so you might as well write the platform specific stuff in an .m file rather than messing around with the .c API for Objective-C. :)

Yes, part of it should be in C. Even if the Objective-C calls were portable (last time I checked GNUStep was pretty much dead) the APIs it calls into aren't. Seems to me like there's more value to just write the Objective-C parts in a .m file normally & call into the shared C/C++ code.

> So why not just write the Objective-C part in C rather than calling the underlying machinery directly.

Because the "underlying machinery" isn't documented by Apple. It may not even be a stable interface!

In fact it basically is:

https://developer.apple.com/documentation/objectivec/objecti...

My understanding of the parent post was that they meant whatever "underlying machinery" AppKit is calling into -- not just the ObjC runtime.

I typo'ed. I meant to say why not right the Objective-C part in Objective-C. I see no value in writing it all in C because you lose all the compile-time checks the compiler is able to perform to catch bugs & the C interface, which AFAIK is ABI stable (would have to be since apps are forward-compatible), is really difficult to use.

I did not mean you can make cross-platform programming thanks to this example but that you may avoid having objective C code in your project thanks to this. I know from personal experience that objective C makes some colleague "nervous" :-)

This is how SDL2 works for Cocoa it also is written in pure-C in some areas where there would normally be Mach files

The Cocoa implementation of SDL 2 uses plain Objective-C to access Apple's APIs: https://github.com/spurious/SDL-mirror/tree/master/src/video...

I couldn't find a call to objc_msgSend in other (.c) files using GitHub's code search. Objective-C and C/C++ are perfectly interoperable, there's rarely a reason to use the verbose and error-prone C API to call into Objective-C.

The .m file extension is not related to Mach: https://stackoverflow.com/a/652266

As I have seen too many times to be surprised now, the source code and setup in assembly is much easier in asm than in higher level languages. Look for ”COM programming with assembler” if you are curious. No casting, no bullshit. Just numbers pushed around :)

I dunno. The massive amount of comments necessary to make this code remotely understandable is pretty telling.

And in one file there was a magic number #1536 or something, never got explained.

Oof, that would have been hard. ;)

More seriously, the "rule against magic constants" makes sense in many circumstances, but there are limits.

Explanation in the form of breadcrumbs:

1. https://github.com/kliment/Printrun/issues/619#issuecomment-...

then

2. https://github.com/gnustep/libs-corebase/blob/master/Headers...

It's more explaining how the whole OS X application model works than the code itself.

Okay, I got curious, but unfortunately that exact book title doesn't seem to exist.

Disclaimer: There are truly some madmen in the world.

Thought: I LOVE THIS! I would love to see a few more even more complicated examples .. wouldn't it be neat if it turns out that its easier to write apps in Assembly than Swift/ObjC, lol ..

I know some people might not like this idea, but I feel more production systems should use some assembly. Although everything is a bit much.

Also of the mindset we should be using more domain specfic languages.

It's a cool stunt, but nothing more. The days of using assembly language in everyday business applications are long gone. Questions of portability immediately come to mind, as well as productivity losses relative to other companies/developers who are producing code faster and more efficiently.

Well, never estimate the power of "hobby". When announcing Linux 27 years ago, Torvalds said "just a hobby, won't be big and professional like gnu". Now name any device and probably someone has ported Linux to it.

In a similar way, probably old-school asm programmers will gather to write mobile app framework in assembly. You know, HTML/JS/Java/Swift is for sissies.

Of course I'm kidding :p

True, if you're writing a typical app, it will probably be easiest for you if you write it in the same manner as most other people.

But if you are doing something very new or unusual, a sample project like this can be invaluable, since it shows the exact set of system calls needed for an app and roughly the minimal code. This is useful if, for example, you're trying to make a new language framework run on iOS (like Swift, Kotlin, or Rust), or if you're trying to answer questions like, "How much of an app's size is unavoidable?"

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