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Additional and Non-Standard AUTO Objects

Klib inheritance and inclusion mechanism changed, this stuff is out of date now.

The Kernel Library has a much-misunderstood feature that allows you to change the effective AUTO object of programs. This document describes how to do it.

In this case, "changing the effective AUTO object" just means having objects implicitly inherit (as with AUTO) from another object. Note that the object being implicitly inherited from, like all objects, will inherit from the AUTO object itself. Obviously, there are some possible problems with cyclic inheritance if you aren't careful here.

First off, you'll need an object manager. Your object manager doesn't have to do anything fancy. It doesn't have to track objects, or respond in any complicated way to any of the function calls it receives. However, it does have to exist and be registered with the Kernel Library via DRIVER->set_object_manager(). See ⁄doc⁄kernel⁄hook⁄driver for details about what functions your object manager needs to define.

Add the line #include "AUTO" to the standard include file, which is usually "⁄include⁄std.h". Create an empty file, called AUTO, in the ⁄include directory. This makes sure that most objects will transparently, automatically include the (empty) AUTO file, which will do nothing.

However, the objects you have specifically chosen to implicitly include your alternate AUTO file are different. You're going to make a file called something like "⁄include⁄second_auto.h". That file contains only the line inherit "⁄usr⁄Bob⁄myauto";

The way you'll choose what objects will use your alternate AUTO object is with your object manager, which will need to contain a call to path_special. Your path_special call will return the filename of your include file (such as "⁄include⁄second_auto.h") when it sees the name of a file that you want to have that second AUTO object.

Please note that your second AUTO object will inherit from the regular first AUTO object, just like any other library. It'll need to be a library (because other programs inherit from it). And make sure it doesn't inherit from itself, and that no libraries it inherits from also inherit from it.

Note that programs under ⁄kernel can't inherit a second AUTO object. You don't get to mess with them. Similarly, nothing under ⁄usr⁄System can get a second AUTO object. They just get the regular one. If you really need objects under ⁄usr⁄System to inherit from your additional AUTO object, you can have them inherit from it explicitly, with an 'inherit' statement, like usual.