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[swarm-hackers] header directory structure

From: Scott Christley
Subject: [swarm-hackers] header directory structure
Date: Sun, 06 Jul 2008 14:34:31 -0700


I recently committed some changes, albeit to the objc runtime branch, that changed how header files are referenced from other header files. For example this:

#import <defobj/DefObject.h>

got changed to this:

#import "DefObject.h"

The reason is due to how frameworks are constructed on Apple (and GNUstep). For those not familiar, frameworks are a simple directory wrapper structure that puts a dynamic library, its header files, documentation, any resource files. Normally on UNIX-like systems, these are separated in difference directories, e.g. the library goes in /usr/local/lib, the header files go in /usr/local/include, the documentation goes in another place as well as the resource files. The nice thing about frameworks is because everything is wrapped up together, it is easy to copy, distribute, move, etc., the framework around and it always has everything together.

However, the design of the framework is fairly rigid, it has a single header directory that *all* headers go into, and it doesn't allow having subdirectories. When programs use a framework, they always reference the framework name as part of #import statement, so for example if my framework was SwarmOSX, then swarm applications would do this:

#import <SwarmOSX/DefObject.h>

So the existing Swarm header files don't work once they get put into the framework, it doesn't know anything about a "defobj" subdirectory. Once possible solution is to use cpp defines to do the appropriate #import like this:

#import <Swarm/DefObject.h>
#import <defobj/DefObject.h>

but personally I think this is pretty ugly and it will need to be done throughout all the header files.

What I would like to suggest is that the UNIX and OpenStep headers are standardized together and that all headers get put into a single Swarm header directory. So instead of this:

#import <defobj/DefObject.h>

it will be:

#import <Swarm/DefObject.h>

for all header files regardless of which Swarm module. Besides keeping a certain degree of source compatibility between Apple, GNUstep, and GNU/Linux systems, another reason (though I have to admit it is pretty weak) is that putting header files in the main include directory, like Swarm does with activity.h, space.h, etc., has the potential to conflict (filename) with other software. By putting everything in a Swarm subdirectory, we are safer with only the "Swarm" name as a potential conflict.

The downside is that when the objc runtime work gets put into the main branch, it will break existing source code. It's not a major change, but does require everybody to change all their #import statements.

what do people think?


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