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.

Answer 2

Another option available is to use a scripting component to your project. One which works quite well is PascalScript. This would allow you to load external scripts after the fact and then run them as needed to interact with your application. As Aaron suggested you will also need to still provide an interface of some sort for your script to interact with your application.

Answer 3

I'm not quite sure what you mean by "alarms", so I'm making a couple of assumptions.

1) If you don't need additional code for the alarms, I would try to make them data driven. Keep the different kinds of alarms in a database or configuration file, which makes it easy to update applications in the field without recompiling or reinstalling.

2) If you need special code for each alarm, you could use run time packages as plug-ins for your application. Search for Delphi runtime packages to get some ideas and tutorials. Here are a couple of links I found:

http://delphi.wikia.com/wiki/Creating_Packages

http://delphi.about.com/od/objectpascalide/a/bpl_vs_dll.htm

3) Scripting, as skamradt already mentioned. If it makes sense for your application, this could also let your customers write their own add-on functionality without requiring a recompile on your part.

Answer 4

You almost definitely want to use Pascalscript, as skamradt suggests. You should start here, and seriously consider this option. There are many possibilities that come out of being able to serialize live code as text. The only downside is possibly speed of execution, but that may not matter for your application domain. I would have upvoted skamradt, but I don't have enough reputation to upvote :)

Answer 5

Some time ago I was looking at a situation sort of like what you're describing.

My answer was .DLLs. I put the variable code in a .DLL that was dynamically loaded, the name specified in a configuration file. I passed in a record containing everything I knew about the situation.

In my case there was only a success/fail return and no screen output, this worked quite well. (It was commanding a piece of machinery.)

Answer 6

This sounds like a place where a scripting language or "Domain Specific Language" may make sense. There are several approaches to this:

• Implement alarm functions in VBscript (.vbs files written in notepad) that accesses your Delphi code via COM API. Using the COM API gives you access to a large range of programming tools for writing functions, including Delphi. This is the most clumsy solution, but easiest to do. It may also be a benefit to your sales process, and it is always good to think about how to sell things.

• Implement your own function language in Delphi. This way you can make it so easy, that your endusers can write their own alarm functions. If you do it as an expression evaluator, you can write an alarm as 2*T1>T2. There are several expression evaluators out there, and you can also write your own if they don't match your needs.

• Use a predefined programming language inside your Delphi application, for instance, "Pascal Script", see http://www.remobjects.com/ps.aspx

Answer 7

You should take a look at PaxCompiler, like PascalScript it allows to load scripts, but you can even precompile them before for more performance. Look at the demos section for the solution of your problem.

As a side note, the web page really looks bad, but the package is really powerful and stable.

Answer 8

I think that the scripting solution it's good for this situation.
There are many scripting packages that you can evaluate:

• Context Scripting Suite
• Fast Script
• RemObjects Pascal Script
• TMS Scripter Studio
• paxScript
• Other packages that you can find on Torry, DSP, VClComponents,...

Regards.

Answer 9

See also Plugins system for Delphi application - bpl vs dll? here on Stackoverflow.