For twenty years, DAX had no way to define your own reusable functions — we copied measure logic around and hoped for the best. That era is over: DAX user-defined functions are now generally available, with typed parameters, optional arguments and full support in web modeling and TMDL.

In this session we'll go from zero to a working UDF library. We'll cover the FUNCTION syntax and type hints, where functions live in the model, and how to design function signatures that survive real-world reuse. The core of the session is a live refactor: we'll take a genuinely messy semantic model — duplicated logic, inconsistent time intelligence, copy-pasted measures — and rebuild it on a small library of UDFs, then version everything with TMDL and Git so your whole team shares one set of functions.

We'll finish with the honest part: performance considerations, current limitations, and how AI assistants like Copilot and Claude can help you generate and test UDFs without introducing subtle bugs.

Level: Intermediate (200–300). Duration: 60 min (45-min cut available). Session can be delivered in English, Spanish or Portuguese.