An extension to the scala's collections library which provides an immutable Map
which has effectively constant lookup time on all operations (including key and index
lookup) while maintaining key ordering.
The default implementation of an scala.collection.immutable.LinkedMap is a
scala.collection.immutable.VectorMap, which is a composite data structure that
internally stores a scala.collection.immutable.HashMap and scala.collection.immutable.Vector.
This is currently the only known practical implementation of such an immutable structure. Equivalent implementations can be seen in libraries such as immutable.js, see here for an example.
Like Scala's standard collection.immutable.Map, scala.collection.immutable.LinkedMap
features specialization for LinkedMap's up to size 4, since small LinkedMap's
are the most likely to be created.
Scala contains an immutable Map which maintains key ordering called a scala.collection.immutable.ListMap.
This is a Map structure which is backed by a linked list, so it will maintain
key ordering however since it is a linked list it will have O(n) time for querying
by index/key.
While using the scala namespace is discouraged, there are certain classes/methods
(such as AbstractMap) which cannot be accessed outside of this package. Linked Map
requires access to these classes for performance/code size reasons.
Linked Map is currently built for Scala 2.10.x, 2.11.x and 2.12.x. 2.13.x is under consideration, as it may make more sense to include an implementation directly in the Scala Collections redesign