We've talked about contracts before, but this week Björn Fahller joins us to give us his thoughts, based on his recent talk at C++ on Sea. This is all pre-Kona - the recent Standards meeting that saw several tweaks to the wording for contracts in the draft standard for C++20. Björn gives us a refresher of what contracts actually are, and how many of us have been using them in some form for years - even decades. Then we discuss what's actually going into C++20, why that's worth having compared to assert() or hand-rolled or library solutions - but also what the shortcomings are - including a couple of weakenesses that have cause some to think that contracts may be "dead on arrival". Where does the truth lie? Björn makes his case and (somewhat boringly) Jon and Phil tend to agree. But what does it matter? The whole show is undefined behaviour, anyway. Special Guest: Björn Fahller. Links: C++ on Sea videos — Now fully uploadedItalian C++ Conference — Andre Alexandrescu keynoting - Saturday June 15, MilanACCU Conference — 2018-10-05 to 2018-10-26 emBo++ — 14th to the 17th of MarchC++ Now — May 5, 2019 - May 10Catch2 2.6.1 releasedWhy You Should Use std::for_each over Range-based For Loops — Jon's guest post on Jonathan Boccara's blogEpisode #32 on Contracts — with John Lakos and Kévin Boissonneault