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Miles Sabin edited this page May 6, 2015 · 20 revisions

shapeless: generic programming for Scala

shapeless is a type class and dependent type based generic programming library for Scala. It had its origins in several talks by Miles Sabin (@milessabin), given over the course of 2011, on implementing scrap your boilerplate and higher rank polymorphism in Scala. Since then it has evolved from being a resolutely experimental project into library which, while still testing the limits of what's possible in Scala, is being used widely in production systems wherever there are arities to be abstracted over and boilerplate to be scrapped.

Contents

Finding out more about the project

A full feature overview of shapeless-2.1.0 is in preparation. In the meantime, please refer to the release notes and the feature overview for shapeless-2.0.0 which can be found here. If you are upgrading from shapeless-2.0.0 you will find the migration guide useful.

shapeless is part of the Typelevel family of projects. It is an Open Source project under the Apache License v2, hosted on github. Binary artefacts are published to the Sonatype OSS Repository Hosting service and synced to Maven Central.

Discussion of shapeless and generic programming in Scala in general happens on the Typelevel mailing list. You will also find many of the main shapeless contributors in its Gitter channel and on IRC in the #shapeless channel on freenode. Questions about shapeless are often asked and answered under the shapeless tag on StackOverflow. Some articles on the implementation techniques can be found on Miles's blog, and Olivera, Moors and Odersky, Type Classes as Object and Implicits is useful background material.

Support for Scala 2.9.x is still available via the shapeless-1.2.4 release (feature overview [here][features124]). It isn't straightforward to bring the latest shapeless features to Scala versions which don't support implicit macros, and this release should be treated as a stopgap until you are able to move your project to Scala 2.11. It might, however, be feasible to backport some of the updates via a compiler plugin for Scala 2.9.x, and anyone interested in contributing or sponsoring such work should get in touch.

Participation

The shapeless project supports the Typelevel code of conduct and wants all of its channels (mailing list, Gitter, IRC, github, etc.) to be welcoming environments for everyone.

Whilst shapeless is a somewhat "advanced" Scala library, it is a lot more approachable than many people think. Contributors are usually available to field questions, give advice and discuss ideas on the Gitter channel, on #shapeless and the mailing list, and for people wanting to take their first steps at contributing we have a selection of open issues flagged up as being good candidates to take on. No contribution is too small, and guidance is always available.

Building shapeless

shapeless is built with 0.13.7 or later. SBT 0.13.6 has an issue related to its new name hashing feature which when compiling shapeless causes SBT to loop indefinitely consuming all heap. Workarounds are to move to an earlier or later SBT version or disable name hashing by adding,

incOptions := incOptions.value.withNameHashing(false)

to your settings.

The master branch of shapeless is built with Scala 2.11.5 by default. To build with Scala 2.10.x you should check out the scala-2.10.x branch. As a general rule all new features and bugfixes are made against master and Scala 2.11.5 and merged into the scala-2.10.x branch with only the minimal changes needed for forwards compatibility.

Contributors

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