How to add code inside a program in runtime (Delphi/Windows)?

Question

I'm working on Windows XP/Delphi 7. I need to add some procedures (or functions) inside a program that is running, and I do not want to re-compile it once again after I finished it.

I just have a host application with 5 functions to send different types of alarms, but there are other new alarm types, so I have to do new functions to send those alarms, but I should not re-build the host application. I have a class named TAlarmManager that it's invoked calling those functions.

Maybe a plugin?? OK, but how can I "insert" new functions??? Tutorial, manual, book, etc.. for learning about this, or any advice on how to do this???

I have studied plugins (I'm totally new on this theme), but no one "talks" about adding functions to a host application. It seems to me that plugins add functionality from itself, I mean, they have been developed with self code to do something, not to "add" code to the host application... How can I do this??

Answer 1

For the technical side: How does the Delphi IDE do it? That would be the first place for me to look.

To understand plugins, you must understand that you can't add new functions. You could but since the old code doesn't know how to call it, they wouldn't be called.

So what you do is you add a "register" or "start" function to your plugin. That start function gets a data structure as parameter which it can examine or extend. In your case, that would be the list of alarms. Alarms always work the same (my guess), so it can add additional alarms.

The main code will then, after registering all plugins, just walk over the list of alarms and invoke the standard alarm function on each of them. It no longer cares where each alarm comes from and what it really does.

The key here: You need to define an interface which both sides subscribe to. The main code calls the interface functions and your plugin code implements them.