How to tell dart to not convert map to <String, String> type and let it be <String, Object&-CodePudding

I have some data which initially is List<Map<String, String>> but in future in some methods calls I have to assign those Map<String, String> elements an <String, dynamic> values. Here is some dart code that shows my intention :

class MyClass {
  String ageGroup = 'some';
  MyClass({required this.ageGroup});
}

void main() {
  var data = [
    {
      'name': 'john',
      'userName': 'john',
    },
    {
      'name': 'john1',
      'userName': 'john1',
    },
  ];

  // JsLinkedHashMap<String, String> in dartpad
  print(data[0].runtimeType);
  
  // after some while
  // throws an error
  data[0]['ageGroup'] = MyClass(ageGroup: 'something');
}

data[0]['ageGroup'] assignment gives me error like this : Error: A value of type 'MyClass' can't be assigned to a variable of type 'String'.

How should I let know dart that don't convert this maps to <String, String> and let it be <String, dynamic> as in future Objects would be the values too.

I have found 1 workaround but I don't want to use it :

void main() {
  var data = [
    {
      'something_random': 123,
      'name': 'john',
      'userName': 'john',
    },
    {
      'something_random': 123,
      'name': 'john1',
      'userName': 'john1',
    },
  ];
  
  print(data[0].runtimeType);
  
  data[0]['ageGroup'] = MyClass(ageGroup: 'something');
}

This works well but I don't want to use it like this....are there any other ways... I have tried .cast<>() and another type castings but still of no use.

CodePudding user response：

By default Dart infers the type of you data literal map.

In your first example there is only String as values so it infers the type List<Map<String, String>>. In the last snippet it infers List<Map<String, Object>> because there are Strings and ints in values of maps.

You can force the type of data by 2 ways:

var data = <Map<String, dynamic>>[...]; // force type of list literal

// or

List<Map<String, dynamic>> data = [...]; // directly type data