Ichoran / collection-strawman

Experimenting with Scala Collections designs for Scala 2.13

Collection-Strawman

Prototype improvements for Scala collections.

• Gitter Discussion
• Dotty Issue
• Scala Center Proposal

Current status

The strawman is available as a regular external library (see below usage instructions). The collections live in the strawman.collection namespace (instead of scala.collection).

Almost all operations and collection types of the current standard collections are available. If you see something missing, please create an issue.

Use it in your project

Add the following dependency to your project:

libraryDependencies += "ch.epfl.scala" %% "collection-strawman" % "0.3.0"

The 0.3.0 version is compatible with Scala 2.13 and Dotty 0.2. Scala 2.12 is also supported but you might encounter type inference issues with it.

We also automatically publish snapshots on Sonatype:

resolvers += Resolver.sonatypeRepo("snapshots")

libraryDependencies += "ch.epfl.scala" %% "collection-strawman" % "0.4.0-SNAPSHOT"

Roadmap

1. September 2017: release targeting Scala 2.13 and Dotty.
   • Implement most of the current collections types
   • Implement most of the current collections operations
   • Alternative to CanBuildFrom to get implicit builders
   • Include tests for correctness (taken from the current collections and from scala-collections-laws)
   • Provide a rewriting tool that migrates a code base from the current collections to the strawman
2. November 2017: move to the scala namespace
   • Create a branch of Scala 2.13 with the strawman instead of the current collections
3. January 2018: new features and performance improvements
   • Add Scala.js support
   • Consider the inclusion of new collection types (such as Spandex, Steque or ArrayDeque)
   • Consider the introduction of new operations (such as database-like joins, variants of groupBy, etc.)
   • Java interoperability
   • Separate project for parallel collections

Contributing

We welcome contributions!

For more information, see the CONTRIBUTING file.

Implemented collection types

• List
• LazyList (aka Stream in 2.12)
• Queue
• Stack
• ArrayOps
• StringOps
• ArrayBuffer
• ImmutableArray (new)
• ListBuffer
• UnrolledBuffer
• LinkedList
• DoubleLinkedList
• Range / NumericRange
• Vector
• HashMap
• TreeMap
• IntMap / LongMap (?)
• ListMap
• MultiMap
• HashSet
• ListSet
• TreeSet
• EqSet
• BitSet
• View

Implemented operations (on the relevant collection types)

Operations not returning a collection

• apply
• contains
• containsSlice
• count
• endsWith
• find
• firstKey
• forall / exists
• foreach
• foldLeft
• foldRight
• get
• getOrElse
• getOrElseUpdate
• head
• indexOf / indexWhere / lastIndexOf / lastIndexWhere / indexOfSlice / lastIndexOfSlice
• indices
• isDefinedAt
• isEmpty / nonEmpty
• keysIteratorFrom
• last / lastOption
• lastKey
• max / maxBy
• min / minBy
• mkString
• product
• reduce / reduceOption / reduceLeft / reduceRight
• size
• span
• startsWith
• sum
• to

Transformations to collections having the same element type

• diff
• distinct
• drop / dropRight / dropWhile
• empty
• filter / filterNot / filterKeys
• groupBy
• init
• intersect
• partition
• range
• rangeImpl
• sorted / sortBy / sortWith
• slice
• splitAt
• substetOf
• subsets
• tail
• take / takeRight / takeWhile
• updated

Transformations to collections that can have a different element type

• combinations
• updated
• prepend
• append
• ++ / concat / union
• ++: / prependAll
• flatMap
• grouped
• keys / keySet / keysIterator
• map / mapValues
• merged
• padTo
• permutations
• scan / scanLeft / scanRight
• sliding
• unzip
• values / valuesIterator
• zip / zipWithIndex

In-place mutating operations

TODO