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The Right Tool for the Job (Shared Objects)
For any task, using the right tool for the job is always a crucial matter. This applies to driving a nail into a wall as much as developing software. And while nobody would ever try to use a glass bottle for the nail, the tools of the trade of the software developer are a bit more abstract (and sometimes, more brittle too).
On AmigaOS the word “shared” is used in two major contexts: Shared Library, and Shared Object. Both are tools for sharing code between applications. However, they have very different methods for doing this, and with that comes a very different approach to using them.
Let’s first look at what they are.
Since the early days of AmigaOS, shared libraries have been a means of sharing code and, to a certain degree, data between multiple users. A shared library is, essentially, a structure in memory called the Library Base, and one or more jump tables to functions that are to be shared. Since Version 4.0 of the OS, these jump tables are called Interface, and although their use differs slightly from their setup in AmigaOS 3.9 and earlier, the principles are the same. A program intending to use a library has to do two steps in order to perform any calls into that library:
