Dynamic Libraries on MacOS X

[Ashley Yakeley]

At 2002-06-10 04:03, Simon Marlow wrote:

>It sounds like frameworks are similar in concept to GHC's packages.

They solve a similar problem in a quite different way. A framework is a 
"bundle": an actual directory with everything inside it, libraries, 
header files, localised strings, whatever, with a particular internal 
structure that does clever stuff with symbolic links to handle multiple 
versions.

Frameworks and other bundles (such as applications) may be relocated by 
the user, though frameworks generally need to be in certain standard 
places so that other tools can find them. Bundles may be uninstalled 
simply by deleting the directory. Generally the Mac GUI shows the 
directory as an object rather than a folder, though there's a special 
menu option to open the directory up like any folder.

By contrast, GHC packages are virtual i.e. the stuff is not necessarily 
all in one directory. And if any of it gets moved, the package.conf file 
would need to be updated.

For code-generating tools, you point to frameworks on the command-line 
much as you do libraries. For instance, just as you do "-lfoo 
-L./foolibs" to refer to libfoo and to search for libraries in 
./foolibs/, you'd do "-framework foo -F ./foofws" to refer to 
foo.framework and to search in ./foofws/ for frameworks (there are also 
standard places to search). The Darwin C compiler can use this to find 
include files, and then you can pass the same options to the linker, and 
it will find the libraries.

Too bad frameworks aren't standard on all UNIX, they are an excellent way 
of packaging software.

>> *) add two command line options that get passed on to the 
>> linker (-framework for linking with a framework and -F for 
>> specifying framework search paths)
>> *) add corresponding entries to package.conf
>
>You mean add a new package for each framework?

I think Wolfgang means add new package specification components, such as 
"frameworks" and "frameworks_dir". They just need to be passed on to the 
linker.

One interesting possibility would be to allow support for .hi files in 
frameworks. This would mean GHC would look inside frameworks specified by 
the -framework flag and "frameworks" package.conf entries for .hi files, 
in addition to -I and "import_dirs". This would mean a bit more code but 
I believe Apple provides APIs for dealing with bundles easily.

-- 
Ashley Yakeley, Seattle WA