ctongfei / gizmos

Cats typeclass-based collection library for Scala (Trees, Graphs, Multimaps and more!)

Poly-collection

Poly-collection is a Scala collection framework that aims to provide an alternative to the standard Scala collection framework. It provides a large range of collection classes, and differs from the standard collection framework in several ways:

• Full support for graphs, trees, multisets, multimaps and others with various functional operators defined on them.

• Based on algebraic typeclasses through the Typelevel Scala family projects Cats, Algebra and Spire (Eq/Order/...). This means the equivalence relation / hashing function for sets / maps can be customized via arbitrary typeclass instances.

• Lazy by default: Higher-order transformational functions are nearly always executed in a non-strict manner: functions like map, filter, flatMap are nearly always evaluated lazily (like Spark). This allows chain application like xs map f filter g reduce h to be much faster than the standard library.

• Returning-same-trait principle: Instead of the uniform-return-type principle of the Scala standard collection library, Poly-collection returns the most fined-grained trait possible without much performance loss. For example, a map applied on an ArraySeq would return a read-only view, or a lazy IndexedSeq instead of a strict ArraySeq.

• Maps and Sets are not Iterables, instead, map.pairs or set.keys are. The nonsensical behavior of zip/tail etc. for Sets/Maps in Scala is removed. map.zip now means zip-by-keys.

• Various algorithms / data structures provided out of the box: binary search, disjoint sets, Fenwick trees, etc.

  • A fully-fledged search subpackage that enables the execution of common search algorithms (BFS, DFS, A*, etc.) on very generic state spaces (of course lazily!).

  • Caching utilities: LRUCache, Memo.

Implicit conversions from/to Scala & from Java collections to Poly-collections are provided by importing the objects poly.collection.conversion.{FromJava, FromScala, ToScala}.

Poly-collection is currently in alpha stage and is progressing into the 0.1 release.

libraryDependencies += "me.tongfei" %% "poly-collection" % "0.1.0"

Pending Scala issues

• SI-2509: Contravariant implicits influences the use of contravariant typeclasses Eq/Order/Hashing.
• SI-2712: Higher-order unification influences the to method on Traversables when piping to a BitSet/DenseIntKeyedMap.

Todo

• Remove Spire from the dependencies.