JSON object wrapper.

json_object.dart

import "dart:core";
import "dart:core" as c;

abstract class _JsonBase<Key> {
  Object _get(Key key, c.bool allowNull);
  List<T> listOf<T>(Key key) => (_get(key, false) as List<Object>).cast<T>();
  Map<String, T> mapOf<T>(Key key) =>
      (_get(key, false) as Map<String, Object>).cast<String, T>();
  JsonObject object(Key key) =>
      JsonObject(_get(key, false) as Map<String, Object>);
  JsonObject objectOrNull(Key key) =>
      JsonObject(_get(key, true) as Map<String, Object>);
  JsonArray array(Key key) => JsonArray(_get(key, false) as List<Object>);
  JsonArray arrayOrNull(Key key) => JsonArray(_get(key, true) as List<Object>);
  String string(Key key) => _get(key, false) as String;
  String stringOrNull(Key key) => _get(key, true) as String;
  c.int int(Key key) => _get(key, false) as c.int;
  c.int intOrNull(Key key) => _get(key, true) as c.int;
  c.double double(Key key) => _get(key, false) as c.double;
  c.double doubleOrNull(Key key) => _get(key, true) as c.double;
  c.num num(Key key) => _get(key, false) as c.num;
  c.num numOrNull(Key key) => _get(key, true) as c.num;
  c.bool bool(Key key) => _get(key, false) as c.bool;
  c.bool boolOrNull(Key key) => _get(key, true) as c.bool;
}

class JsonObject extends _JsonBase<String> {
  final Map<String, Object> map;
  JsonObject(this.map);
  Object operator [](String key) => map[key];
  Object _get(String key, bool allowNull) {
    var object = map[key];
    if (object == null) {
      if (map.containsKey(key)) {
        if (!allowNull) throw CastError("Value of key $key is null");
      } else {
        throw ArgumentError.value(key, "key", "Not in the map");
      }
    }
    return object;
  }
}

class JsonArray extends _JsonBase<int> {
  final List<Object> list;
  JsonArray(this.list);
  int get length => list.length;
  Object operator [](int key) => list[key];
  Object _get(int key, bool allowNull) {
    RangeError.checkValidIndex(key, list, "key", list.length);
    var object = list[key];
    if (object == null && !allowNull) {
      throw CastError("Value at index $key is null");
    }
    return object;
  }
}

class CastError extends c.CastError {
  String _message;
  CastError(String message) : _message = message;
  String toString() => "CastError: $_message";
}

// Example
main() {
  var obj = {"a": [1, 2.3, true, "s", null, [4], {"x": 5}],
             "b": {"x": 6},
             "c": 7,
             "d": 8.9,
             "e": false,
             "f": "s",
             "g": null};
  var js = JsonObject(obj);
  print(js.array("a").int(0));
  print(js.array("a").double(1));
  print(js.array("a").bool(2));
  print(js.array("a").string(3));
  print(js.array("a").stringOrNull(4));
  print(js.array("a").array(5).int(0));
  print(js.array("a").object(6).int("x"));
  print(js.object("b").int("x"));
  print(js.int("c"));
  print(js.double("d"));
  print(js.bool("e"));
  print(js.string("f"));
  print(js.stringOrNull("g"));
}