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New things in Dart 3

Following are the new important/interesting things introduced starting from Dart 3.0.

Records

New built-in type in Dart 3 which is immutable. Like any other collection types, it lets you bundle multiple objects in a single opject.

var record = (1, a: "2", b: 3);

record.$1; // 1
record.a; // "2"

When is it useful? Mostly, when you want multiple return types.

Example:

Suppose we have a json response from an API call:

{
  "name": "John Doe",
  "age": 30,
}

Previously we would either use a List<Object> or create a class with name and age to get both the values, which of course had some drawbacks.

We would do:

List<Object> getUserInfo(Map<String, dynamic> json){
    return [json['name'], json['age']];
}

OR

class UserInfo{
    final String name;
    final int age;

    UserInfo({required this.name, required this.age});
}

UserInfo getUserInfo(Map<String, dynamic> json){
    return UserInfo(name: json['name'], age: json['age']);
}

The first approach is not ideal as it relies on the position of values in a list, which can be error-prone and hard to maintain. Similarly, the second approach of creating a separate class for just two values can be overly verbose and unnecessary.With the introduction of records in Dart 3, a more concise and safer solution is available.

We can used named records to get the same result as above:

({String name, int age}) userInfo(Map<String, dynamic> json) {
  return (name: json['name'] as String, age: json['age'] as int);
}

print(userInfo(json).name); // John Doe

Other use case might be controlling flow of arguments:

Find more at: - https://dart.dev/language/records

Pattern Matching and Code Destructuring

Imagine having a switch case like below:

 final a = 40;

  switch(a){
    case >=10 && <=50:
      print('a is greater than 10');
      break;
  }

Or being able to do this:

var numList = [1, 2, 3];
var [a, b, c] = numList;

print(a); // 1

Or this:

(lat, long) getLatLong() => (40.7128, 74.0060);
print(getLatLong().lat); // 40.7128

Well, you can do it now with Dart 3.0 and reading the links below will show you much more you can do now.

You can get more used it by doing the exercise below: https://codelabs.developers.google.com/codelabs/dart-patterns-records#0

Class Modifiers

Dart 3.0 introduces us to Fiveeee new class modifiers to allow an author to control whether the type allows being implemented, extended, and/or mixed in from outside of the library where it's defined. Check the links below to find out about new modifiers.

To understand more about the WHY/WHEN_TO USE about the new class modifiers:

Enhanced Enums (Was in Dart 2.17 but wanted to include it here)

Enums are now more powerful than ever. You can now add methods, properties, and constructors to enums.