C# 8 as prior art

[rbuckton]

C# 8 (as of Preview 5) has added a new index and slice notation ([1], [2]):

• An Index type (System.Index) that specifies an offset and direction.
• The ^n syntax to specify an offset from the end of a sequence (array, etc.).
  • ^n is shorthand for new Index(n, true)
• The Range type (System.Range) that specifies a start/end Index in a sequence.
• The x..y range operator.
  • x..y is shorthand for new Range(new Index(x), new Index(y))
  • ..y is shorthand for new Range(Index.Start, new Index(y))
  • x.. is shorthand for new Range(new Index(x), Index.End)
  • .. is shorthand for new Range(Index.Start, Index.End)

Also, since the ^ operator is currently only an infix operator, perhaps a ^ prefix operator might be worth considering for this proposal as well.