How to divide a Delphi project into BPLs properly?

Question

The company I work for develops a system in Delphi, that contains dozens of exe modules, and each of them is identical to a certain degree if it comes to source code. Sadly,

Answer 1

Imagine you have a project with an EXE and two different BPL modules, and somewhere in that codebase, there's a line that says if MyObject is TStringList then DoSomething;. The is operator works by examining the object's class metadata, stored in the VMT, and then following a chain of VMTs through the ClassParent pointer, to see if any of them match the class reference (also a VMT pointer) for TStringList. In order to make sure that this will work correctly, there needs to be one single VMT for TStringList that's the same throughout your entire program, no matter how many BPLs it's divided up into, which means it has to be in its own package. That's why system runtimes like rtl*.bpl and vcl*.bpl are necessary, and there's not much you can do about that. It's part of the price of using BPLs.

As for not being able to debug, you need to make sure that the BPLs are built with debug info enabled and that the debugger knows how to find the folder where the DCP (the file containing the debug info for the BPL) is located. And you won't be able to trace into system BPLs, because debug-enabled DCPs weren't shipped with your version. They were added pretty recently, I think in XE but it might have been in D2010.