Adam does iOS "goodbye world"

Posted 2019-10-07

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What Adam is working on

So much stuff these last few days.

cgi.d has compatibility with Musl libc Linux builds now, both plain cgi mode and embedded_httpd_threads tested successfully. Had to fight druntime's overly-conservative Posix headers, and Phobos' LockingTextWriter not working. But was able to work around them thanks to the help of bug2000 on irc.

dom.d, simpledisplay.d, and a few others tested in gdc. They work. Alas cgi.d does not... static foreach was too alluring. I might come back to it.

I also played with ldc for android. I'll write about that next week.

But the big thing is mere minutes ago, I got D working on iOS! Well, sort of. Let's get into the details.

D on iOS

The D Foundation is looking for someone to do this, and I said no because I didn't think I could do it. But I had to set up some osx vm stuff for simpledisplay development anyway... and since it was sitting there, the allure made me spend today on messing with xcode anyway.

Step 1: build a hello world with objective C. Took forever to download all the spam, but it worked!

Step 2: add a button to it. Again, took WAY longer than it probably should have since I know literally nothing about this (I couldn't even find the menu bar for a while LOL), but got it in. Had it call a ViewController method. Since I don't know anything about iOS, I just had it write to a null pointer. When it crashed successfully, I rejoiced.

Step 3: make the controller call a C function that crashed. Easy enough, though adding the .o file was kinda a pain. Had to add it to the xcode project... then add it again, since apparently the first time only added it to the file list, not the build. Oh well.

Step 4: move that from a C file to a D file, with extern(C). Trivial. Actually, even dmd was able to do it! (The iPhone simulator in Xcode actually runs x86_64 code. And there was much rejoicing.)

Step 5: move that ViewController's implementation over to D, using extern(Objective-C). Failed. Failed. Failed. I almost gave up, then I started to xxd test.o.

This is where things got interesting: the storyboard thing complained it couldn't find the ViewController class. Yet I'd get linker errors on duplicate definition if I did it in D and ObjC. Why oh why could it not find what was obviously there?

Turns out D's objective C glue wasn't outputting one specific detail needed. Time to hack dmd's source and add it in... compile... and OMG THE D CLASS GOT CALLED.

This is huge. Now, knowing this works, I can take further steps - defining that view class means I can define *any* class in D and have it work. It means we can use xcode for the interface designer and final linking but not the main code (you just bring in the object file from the outside, and I believe we can have Intel and ARM builds in the same file). Can probably even copy the commands out of xcode and cut it off entirely if we want.

I'll see about putting my dmd change upstream later, then see if we can use ldc to actually generate the arm code too. Probably compile the D runtime on it too... hopefully it is similar enough to osx that a cross compile is reasonable.

Took a LOT longer than I thought but this success is very encouraging.