How do you continue to develop large (long-term) software systems with outdated and new code?

Question

I am working on a large code base with a large database for users. The code was originally written in vb6 with several C ++ COM modules for low-level operation.

It is completely impossible to rewrite all the code that is already written in vb6 and is used by our customers every day, but we also continue to improve and customize the software (large and small).

My solution so far is to write most of the new code in C # (winforms and even wpf now), and then use COM interop to call modules from vb6.

Does anyone have experience with long-term software packages like this (10+ years) that cannot be stopped for a complete rewrite, but this requires constant new development at the same time. In addition, in mixed systems, how is it, what is the best way to interact with modules? I am using COM right now, but also reviewed IPC with separate processes.

Answer 1

It is difficult to give one comprehensive answer, but the high-level approach is clear. At least this is the approach I used. Priority of your goals, and then try to determine the costs of achieving these goals. Your costs essentially boil down to "developer time."

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