Announcement: cats 1.0.0

by Kailuo Wang on Dec 25, 2017


The cats maintainer team is proud to announce the cats 1.0.0 release. Cats has been striving to provide functional programming abstractions that are core, modular, approachable and efficient. Cats 1.0.0 marks the point where we believe that our API is robust and stable enough to start guarantee backward binary compatibility going forward until Cats 2.0. We expect the Cats 1.x series to be fully backwards compatible for at least one year. This is a major milestone towards our goal of providing a solid foundation for an ecosystem of pure, typeful functional libraries.


The vast majority of changes since 1.0.0-RC1 are API compatible, with scalafix scripts ready for those that do not. Here is the change list and migration guide.

Binary compatibility

After 1.0.0 release, we’ll use the MAJOR.MINOR.PATCH Semantic Versioning 2.0.0 going forward, which is different from the EPOCH.MAJOR.MINOR scheme common among Java and Scala libraries (including the Scala lang). In this semantic versioning, backward breaking change is ONLY allowed between MAJOR versions. We will maintain backward binary compatibility between PATCH and MINOR versions. For example, when we release cats 1.1.0, it will be backward binary compatible with the previous 1.0.x versions. I.E. the new JAR will be a drop-in replacement for the old one. This is critical when your application has a diamond dependency on Cats - depending on two or more libraries that all depend on Cats. If one library upgrades to the new 1.1.0 Cats before the other one does, your application still runs thanks to this backward binary compatibility.

We will also consider using organization and package name for MAJOR versioning with binary breaking changes in the future. But that decision is yet to be made.


Cats is built for the FP Scala community by the FP Scala community. We can’t thank enough to our 190 (and growing) contributors and our users who provided feedbacks and suggestions.
Congratulations to all of us. Let’s celebrate this exciting milestone together.