Have you ever imagined array[0.5]? here is the answer

devilsnest.dart

// encoding: utf-8
import "dart:io";

enum ExportDirection {
  Integer,
  Double
}

class HybridIndex {
  final int integer;
  final double realnum;
  final ExportDirection _direction;

  HybridIndex({ExportDirection d = ExportDirection.Integer, int integer = 0, double realnum = 0.0}) :
    this.integer = integer,
    this.realnum = realnum,
    this._direction = d;

  dynamic export() {
    switch (_direction) {
      case ExportDirection.Double:
        return realnum;
      default:
        return integer;
    }
  }
}

class DevilsNest<T extends int> {
  List<T> _internal;
  int get length {
    return _internal.length;
  }

  DevilsNest() {
    _internal = new List<T>();
  }

  void add(T a) {
    _internal.add(a);
  }

  void addAll(Iterable<T> i) {
    _internal.addAll(i);
  }

  T operator[](HybridIndex hi) {
    var index = hi.export();
    if (index is double && index == 0.5) {
      return _internal[index.floor()] ^ _internal[index.ceil()];
    }

    return _internal[index];
  }
}

void main(List<String> args) {
  var array = new DevilsNest();
  args.forEach((arg) => array.add(int.parse(arg)));

  if (array.length < 2) {
    print("Program needs more than two integers. halted");
    exit(-1);
  }

  print("array[0] = ${array[new HybridIndex(d: ExportDirection.Integer, integer: 0)]}");
  print("array[1] = ${array[new HybridIndex(d: ExportDirection.Integer, integer: 1)]}");
  print("array[0.5] = ${array[new HybridIndex(d: ExportDirection.Double, realnum: 0.5)]}");
}