With the addition of Unions and closed class hierarchies, C# 15 is set to be the most impactful new version in a very long time. This new syntax will allow for true exhaustive matching and remove countless lines of boilerplate much the same as how nullable reference type have done for us already.

This talk takes you over everything you need to know to hit the ground running when C#15 when dotnet 11 is released in November. This includes the what and the why's of unions and closed class hierarchies, as well as some of the more nitty gritty implementation tricks to really kit out your union definitions.

Further more we will step into the future of C# and how Discriminated unions through possible future draft specifications could change how you write dotnet forever. With this one last piece C# could unlock language level Result types as-well as a whole plethora of syntactical sugar that change how C# devs structure their code. I will take you through an example of what this could look like and ho will completely eliminate an entire class if runtime errors.

Why write business logic littered with exception handling when almost all of it can be eliminated through compiler level guarantees. Closed types (including unions) might feel insignificant, but soon they very well could turn into the killer feature of C#