In the code below, and other instances in this file, it looks like a typo where == was used instead of =. https://github.com/sgbush/cppcon2022/blob/8b13be4056c596a4f2c9e932fd15c5e7421778f5/code/sections/3_developer_friendly_address_like/uuid.hpp#L53 BTW really liked this talk at CppCon 2022. Thanks.