Two days, built for engineers.

Sourcecode translation as a step in Legacy Modernization

Leszek Włodarski

Legacy Systems are not a myth, they are all around us, just not visible to modern developer. How to make a transformation of those big, usually critical and crucial systems is a riddle that almost nobody can solve, except mBank. The talk would be an inspiration of how automated sourcecode translation might be the solution for one of the obstacles at the legacy system modernization path. What steps have we taken to finally switch 3m LoC into modern platform with success: • Translation models o Low level .NET translation o Logical kind of DSL approach … the runtime o What about a compilers … • Sourcecode translation built from 3 steps o Preprocessing o Translation to .NET o Postprocessing • Start small – unit tests • Grow bigger – functional tests • Pilot and run .NET for new stuff • Comparison tests • Run everything And the pros&cons of such an approach in context of: • quality & test automation • people transformation • effort needed to maintain such a platform • effort and capabilities to make translation work • performance tunning • tools and libraries available The story based on CORE Banking system transformation, so heavy, critical system – the heart of the Bank, nothing simple and small. mBank was awarded by Forrester https://www.forrester.com/blogs/forresters-2025-technology-strategy-impact-award-winner-and-runners-up-for-emea/ and by CIO.NET Poland organization https://www.linkedin.com/posts/brush_digital-excellence-awards-2025-za-przebudow%C4%99-activity-7397562530610544640-B31l/?originalSubdomain=en for this Replatforming/Transformation project. The projects itself it was 9 years of work and we just did it