Imms has several variations for indexing.
Negative Indexing
Imms collections support negative indexing, a feature borrowed from other languages such as Python. In this system, -1 denotes the last index, -2 the one before that, and so forth.
You can pass a negative index wherever you can pass any kind of index, including CopyTo, this[int], and others. You can’t pass negative numbers to methods like Take because they expect a count rather than an index.
Negative indexing is particularly helpful when slicing a collection. For example, this[0, -4] returns the collection minus the last 3 items, while this[-4, -2] returns a slice consisting of the 4th, 3rd, and 2nd items from the end.
Sort order indexing
For sorted collections, such as ImmSortedSet and ImmSortedMap, you can retrieve items by their index in the sort order using the method ByOrder(int index). ByOrder(0) corresponds to the minimum and ByOrder(-1) corresponds to the maximum.
Slices
For sequential collections, you can retrieve a slice of the collection using the indexer this[int start, int end]. For example, ImmList.Of(1, 2, 3)[0, 1] returns a list consisting of the first two elements.
For sets and maps, you can instead use the Slice(TKey start, TKey end) method, which returns a slice of the collection with keys between start and end. They keys themselves don’t have to be part of the collection, but they are included if they are.