Better ImmutableList

[wadoon]

Issue

We currently have two implementations of immutable sequences with ImmutableList and ImmutableArray. This requires conversions sometimes, but mainly it leads to confusion about which implementation should be taken.

Intended Change

This PR unifies everything under ImmutableList.

There are two fresh children classes: ImmutableListArray and ImmutableListList. Both behave like ImmutableList, but use different data storage (T[] or List<T>) in the background.

Some operations from ImmutableList are quite expensive on this data storages, e.g., tail() or reverse(). Therefore, I introduced views that emulate these operations, without copying the data, i.e.,

• ImmutableListConcat as ImmutableList#prepend(other)
• ImmutableListReverse for ImmutableList#reverse()
• ImmutableListSubList for ImmutableList#take(n), ImmutableList#skip(n), ImmutableList#tail()

These operations are now in $O(1)$.

The class ImmutableArray should be considered obsolete.

Developers should use only the methods and functions of ImmutableList. Implementation may override them if there is a faster implementation, e.g, tail() on ImmutableSList.

Plan

• Renaming ImmutableSList to ImmutableList.
• More, even more test cases, coverage is not so bad, but could be better.
• Update the JavaDoc documentation

Type of pull request

• Refactoring (behaviour should not change or only minimally change)

• New feature (non-breaking change which adds functionality)

• There are changes to the (Java) code

Ensuring quality

• I made sure that introduced/changed code is well documented (javadoc and inline comments).