Join patterns are a high-level programming construct for message-passing applications. They offer an intuitive and declarative approach for specifying how concurrent and distributed components coordinate, possibly depending on complex conditions over combinations of messages.

This talk illustrates JoinActors, a library for Scala 3 for programming actor-based applications using a native-looking join pattern matching API. The talk will discuss how JoinActors leverages the Scala 3 metaprogramming capabilities, the challenges in defining and implementing a deterministic and performant join pattern matching algorithm, and how JoinActors’s modular design allows for experimenting with different algorithm optimisations.