Good Evenening Ladies and Gentlemen!



== Background ==
So I currently have a bare-bones Cocoa-app. It's just a window with an OpenGL-view. In the view's draw-function I make the gl-view the current OpenGL context and then call "extern (C) render()". Meanwhile, in a D-file I have the implementation for this function. Here I've copied all the function names from opengl.h and declared them in the D-file ("extern (C) glBlabla()" etc) so I can call glBegin etc from my render()-function in D. This is all in XCode and I use Michel Fortin's "D for XCode"-plugin btw.

This works great! The window paint triangles and what have you. Pretty! Happiness!

But, sometimes I get reeeaally weird bugs. I had one bug where if I added an empty function to a class in D I got EXC_BAD_ACCES (segfault). An empty function! Ie "void f(){}". Remove the function--it works. In the debugger, I got the impression maybe the stack has got messed up, but I don't know, the debugger just shows assembler code, and I don't have the proper skills.

This got really frustrating, needless to say, so I started playing around with the build settings. I switched from using LLVM 1.5 (for the obj-c code) to gcc 4.2. And now it magically seems to work!

Ok. But as you might understand, the frustration is not quite gone. Adding a function now feels like a spinning a wheel of fortune. It's utterly demoralizing. So I thought about this and realized, I probably should try to find out what it is I'm actually doing here, and hear with some real programmers if there's a "proper" way of doing it. So my question, dear D community:



== Question ==
How do you make D code and Obj-C code coexist? That is, I want to write a Cocoa-app that is mostly written in D, and with a little "glue"-code in Objective-C. How do you set that up? Is it even supposed to be possible?

(And what could the bug above be? I know LLVM does link-time optimizations, and even run-time optimizations. Could it be that it messes things up?)



BR
/HF

On 2010-10-05 10:02:45 -0400, Heywood Floyd <soul8o8@gmail.com> said:

> But, sometimes I get reeeaally weird bugs. I had one bug where if I added an empty function to a class in D I got EXC_BAD_ACCES (segfault). An empty function! Ie "void f(){}". Remove the function--it works. In the debugger, I got the impression maybe the stack has got messed up, but I don't know, the debugger just shows assembler code, and I don't have the proper skills.

It's hard to say without further details, but it could be that you're not recompiling everything that uses the class where you add a function. Unlike in Objective-C, adding a function to a D class breaks most compiled code that uses that class (because you're adding an offset to the virtual function table), so you need to recompile every D module that uses that class (or a derived class).

Note that this is totally unrelated to having Objective-C code in the same program.


> This got really frustrating, needless to say, so I started playing around with the build settings. I switched from using LLVM 1.5 (for the obj-c code) to gcc 4.2. And now it magically seems to work!

Are you using D for Xcode? By doing that you basically force everything to be recompiled, which solves problem described above.


> [...]
> 
> == Question ==
> How do you make D code and Obj-C code coexist? That is, I want to write a Cocoa-app that is mostly written in D, and with a little "glue"-code in Objective-C. How do you set that up? Is it even supposed to be possible?

It is totally possible, and not that hard. Communicating via `extern (C)` functions should work well.


> (And what could the bug above be? I know LLVM does link-time optimizations, and even run-time optimizations. Could it be that it messes things up?)

I doubt LLVM optimizations have anything to do with your problem. Things to keep in mind when mixing Objective-C:

1. Apple's Objective-C GC isn't supported by D, so you it's probably safer to use manual memory management (retain/release) on the Objective-C site.

2. Exceptions are not compatible between the two runtimes. Throwing can cause unexpected results when it unwinds stack frames in the other language.


-- 
Michel Fortin
michel.fortin@michelf.com
http://michelf.com/

Ok! Thanks for the advice! Great work on the plugin—it got me into D :)

/FH

Michel Fortin Wrote:

> On 2010-10-05 10:02:45 -0400, Heywood Floyd <soul8o8@gmail.com> said:
> 
> > But, sometimes I get reeeaally weird bugs. I had one bug where if I added an empty function to a class in D I got EXC_BAD_ACCES (segfault). An empty function! Ie "void f(){}". Remove the function--it works. In the debugger, I got the impression maybe the stack has got messed up, but I don't know, the debugger just shows assembler code, and I don't have the proper skills.
> 
> It's hard to say without further details, but it could be that you're not recompiling everything that uses the class where you add a function. Unlike in Objective-C, adding a function to a D class breaks most compiled code that uses that class (because you're adding an offset to the virtual function table), so you need to recompile every D module that uses that class (or a derived class).
> 
> Note that this is totally unrelated to having Objective-C code in the same program.
> 
> 
> > This got really frustrating, needless to say, so I started playing around with the build settings. I switched from using LLVM 1.5 (for the obj-c code) to gcc 4.2. And now it magically seems to work!
> 
> Are you using D for Xcode? By doing that you basically force everything to be recompiled, which solves problem described above.
> 
> 
> > [...]
> > 
> > == Question ==
> > How do you make D code and Obj-C code coexist? That is, I want to write
> > a Cocoa-app that is mostly written in D, and with a little "glue"-code
> > in Objective-C. How do you set that up? Is it even supposed to be
> > possible?
> 
> It is totally possible, and not that hard. Communicating via `extern (C)` functions should work well.
> 
> 
> > (And what could the bug above be? I know LLVM does link-time optimizations, and even run-time optimizations. Could it be that it messes things up?)
> 
> I doubt LLVM optimizations have anything to do with your problem. Things to keep in mind when mixing Objective-C:
> 
> 1. Apple's Objective-C GC isn't supported by D, so you it's probably safer to use manual memory management (retain/release) on the Objective-C site.
> 
> 2. Exceptions are not compatible between the two runtimes. Throwing can cause unexpected results when it unwinds stack frames in the other language.
> 
> 
> -- 
> Michel Fortin
> michel.fortin@michelf.com
> http://michelf.com/
>