What is swave?

swave is a library providing a general, Reactive-Streams-compliant streaming infrastructure for applications written in Scala. As such it plays in the same space as Akka-Stream, but differs from it in some important aspects. (For more info on this check out swave vs Akka-Stream.)


The requirements imposed on today’s software are manifold. Apart from simply “working” the applications we write are supposed to be responsive, resilient and elastic (as defined, for example, by the Reactive Manifesto). Additionally they are expected to digest ever-growing data volumes and make efficient use of their increasingly parallel and distributed hardware basis. All this presents significant challenges, which fuel the continuing search for programming models that are attractive and advantageous in today computing environments.

One such programming model, although hardly a recent invention at its core, is Stream Processing.

Scala provides the scala.immutable.Stream datatype with its standard library but this abstraction is quite limited in its functionality and barely scratches the surface of the benefits that Stream Processing as a programming abstraction is able to provide. Therefore a number of stream processing libraries have recently emerged in the Scala eco-system, the most prominent of which are probably Akka-Stream and FS2 (formally Scalaz Stream), which approach the field from two different angles.

Since modern stream processing, especially with support for non-blocking backpressure, is both incredibly sexy and still relatively new, with plenty of learnings still to be unearthed, we believe that there is more than enough space for a few more approaches to be tried and tested before settling on one or two “standard implementations”.

swave attempts to be just that: A stream processing implementation, purely in and for Scala, which further explores the boundaries of the possible, sometimes by being intentionally different.

Design Principles

swave’s design is guided by the following principles:

swave’s internal mechanics as carefully crafted for excellent performance in high-load environments. Apart from being fully non-blocking this also entails a focus on limiting allocations (and thereby GC pressure).
The type-heavy DSL is designed to add almost no runtime overhead.
All dependencies are very carefully managed, swave’s codebase itself is kept as lean as possible.
Conceptually Simple
Being effective at writing stream-based logic can take some getting used to. swave tries to make this as easy as possible by only introducing concepts that are absolutely essential.
As with any new programming model you’ll likely spent the large majority of your time debugging code that doesn’t (yet) quite do what you expect it to. Making this task as easy as possible is one of swave’s key focus points.
Type-Safe and Concise
Being written in and for Scala a type-safe API is naturally key. swave tries to let the compiler statically verify as much of your program logic as possible while reducing necessary boilerplate to the absolute minimum.