foo1.cs

    public RangeKind RangeKind
    {
      get
      {
        var hasStartIndex = LeftOperand != null;
        var hasEndIndex = RightOperand != null;

        if (hasStartIndex)
        {
          return hasEndIndex ? RangeKind.FromStartToEnd : RangeKind.FromStart;
        }
        // else
        {
          return hasEndIndex ? RangeKind.ToEnd : RangeKind.Full;
        }
      }
    }

foo2.cs

    public RangeKind RangeKind
    {
      get
      {
        switch (LeftOperand, RightOperand)
        {
          case ({ }, { }): return RangeKind.FromStartToEnd;
          case ({ }, null): return RangeKind.FromStart;
          case (null, { }): return RangeKind.ToEnd;
          case (null, null): return RangeKind.Full;
        }
      }
    }

foo3.cs

    public RangeKind RangeKind
    {
      get
      {
        return (LeftOperand, RightOperand) switch
        {
          ({ }, { }) => RangeKind.FromStartToEnd,
          ({ }, null) => RangeKind.FromStart,
          (null, { }) => RangeKind.ToEnd,
          (null, null) => RangeKind.Full
        };
      }
    }

public RangeKind RangeKind => switch (LeftOperand, RightOperand)
{
    case ({ }, { }): return RangeKind.FromStartToEnd;
    case ({ }, null): return RangeKind.FromStart;
    case (null, { }): return RangeKind.ToEnd;
    case (null, null): return RangeKind.Full;
}

@aensidhe That one is not supported :)
switch (LeftOperand, RightOperand) is a statement, while expression body requires expression. Also semicolon at the end is missing :D
The correct option will be like this:

public RangeKind RangeKind => (LeftOperand, RightOperand) switch
{
    ({ }, { }) => RangeKind.FromStartToEnd,
    ({ }, null) => RangeKind.FromStart,
    (null, { }) => RangeKind.ToEnd,
    (null, null) => RangeKind.Full
};