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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 feature overview of shapeless-2.0.0 can be found [[here|Feature-overview:-shapeless-2.0.0]]. If you are upgrading from shapeless-1.2.4 you will find the [[release notes|Release-notes:-shapeless-2.0.0]] and [[migration guide|Migration-guide:-shapeless-1.2.4-to-2.0.0]] useful.

shapeless is part of the typelevel family of projects along with Scalaz and Spire. 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.

The project is currently at the first milestone release of shapeless-2.0.0 and if you are starting to investigate shapeless it is recommended that you start there: a final shapeless-2.0.0 release is expected before the end of 2013. shapeless-2.0.0 takes advantage of the availability of implicit macros in Scala 2.10.2 to reduce, and in many cases completely eliminate, the already minimal boilerplate that remained in earlier releases.

There is a mailing list for discussion around generic programming in Scala in general and shapeless in particular. You will also find many of the main shapeless contributors 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|Feature-overview:-shapeless-1.2.4]]). 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 2.10. 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.

Using shapeless

Binary release artefacts are published to the Sonatype OSS Repository Hosting service and synced to Maven Central. Snapshots of the master and scala-2.10.x branches are built using Travis CI and automatically published to the Sonatype OSS Snapshot repository. To include the Sonatype repositories in your SBT build you should add,

resolvers ++= Seq(
  "Sonatype OSS Releases"  at "http://oss.sonatype.org/content/repositories/releases/",
  "Sonatype OSS Snapshots" at "http://oss.sonatype.org/content/repositories/snapshots/"
)

shapeless-2.0.0

Builds are available for Scala 2.11.0 and later and for Scala 2.10.4.

// For Scala 2.11.0
scalaVersion := "2.11.0"

libraryDependencies ++= Seq(
  "com.chuusai" %% "shapeless" % "2.0.0"
)

For Scala 2.10.x you must specify a Scala version of at least 2.10.2, and add either cross CrossVersion.full or provide an explicit Scala version suffix to your shapeless dependency,

// For Scala 2.10.x >= 2.10.2
scalaVersion := "2.10.4"

libraryDependencies ++= Seq(
  "com.chuusai" % "shapeless_2.10.4" % "2.0.0"
  // "com.chuusai" % "shapeless" % "2.0.0" cross CrossVersion.full  // Alternatively ...
)

Note that Scala 2.10.x releases are compatible with each other starting from 2.10.2, so a mismatch in minor versions above would be fine.

shapeless-2.1.0-SNAPSHOT

Builds are available for Scala 2.11.0 and Scala 2.10.4. The main line of development for shapeless 2.1.0 will be Scala 2.11.0 with Scala 2.10.x supported via the macro paradise compiler plugin.

scalaVersion := "2.11.0"

libraryDependencies ++= Seq(
  "com.chuusai" %% "shapeless" % "2.1.0-SNAPSHOT" changing()
)

Note that for Scala 2.10.4 you must provide an explicit Scala version suffix to your shapeless dependency,

scalaVersion := "2.10.4"

libraryDependencies ++= Seq(
  "com.chuusai" % "shapeless_2.10.4" % "2.1.0-SNAPSHOT" changing()
)

shapeless-1.2.4

Builds are available for Scala 2.9, 2.10 and 2.11.0. If you are working with Scala 2.10.2 or later you should use shapeless-2.0.0 instead.

If your project is built with Scala 2.9.3 or earlier, then you will need to specify the -Ydependent-method-types compiler flag,

scalaVersion := "2.9.3"

scalacOptions += "-Ydependent-method-types"

libraryDependencies ++= Seq(
  "com.chuusai" %% "shapeless" % "1.2.4"
)

This option isn't necessary or supported in Scala 2.10 and later, so you should omit it if you are building with Scala 2.10.2 or later,

scalaVersion := "2.10.4"

libraryDependencies ++= Seq(
  "com.chuusai" %% "shapeless" % "1.2.4"
)

If you want to be able to support building relative to both 2.9.3 and 2.10 and later then you should use the 2.10.4 configuration above and add the following,

scalacOptions <++= scalaVersion map { version =>
  val Some((major, minor)) = CrossVersion.partialVersion(version)
  if (major < 2 || (major == 2 && minor < 10)) 
    Seq("-Ydependent-method-types")
  else Nil
}

which will set the -Ydependent-method-types compiler flag conditionally on the actual Scala version in use.

Building shapeless

shapeless is built with SBT 0.13.2. The master branch is built with Scala 2.11.0 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 2.11.0 and merged into the scala-2.10.x branch with only the minimal changes needed for forwards compatibility.

Contributors