It contains some basic concepts of dart language that is needed for flutter app developement.

A factory constructor is a special type of constructor in Dart that allows you to create objects without using the new keyword. Instead, you can use a named constructor to define how the object should be created.

To use a factory constructor, you must first define the constructor as factory. Then, you can use the constructor to create objects just like any other constructor.

📝 Example:

class MyClass {
  final String name;
  final int age;
  
  MyClass(this.name, this.age);
  
  factory MyClass.fromMap(Map<String, dynamic> map) {
    final name = map['name'] as String;
    final age = map['age'] as int;
    return MyClass(name, age);
  }
}

The main benefit of using a factory constructor is that it allows you to control the object creation process. You can perform any necessary calculations or data validations before returning the object. This can help you write more efficient and error-free code.

🚀 Another benefit is that it allows you to return a cached instance of an object instead of creating a new instance every time. This can be useful if you need to create many instances of an object and want to avoid the overhead of creating new instances.

• ⚡️ Efficient object creation process.
• 🛡️ Controlled data validations.
• 🔄 Ability to return cached instances.

var variable once assigned the type can not change.

  void main() {
  var a = 10;
  print(a);
  a = 'Bob';
  print(a);
  a = 'c';
  print(a);
  a = 1.00012;
  print(a);
}

The above code will show error.

dynamic variable once assigned the type can be changed.

void main() {
  dynamic a = 10;
  print(a);
  a = 'Bob';
  print(a);
  a = 'c';
  print(a);
  a = 1.00012;
  print(a);
}

But this code will run. Here is the output:

10
Bob
c
1.00012

void main() {
  final values = giveMeSomeDoubles();
  print(values.point);
  print(values.greeting);
}

({double point, String greeting}) giveMeSomeDoubles() {
  return (point: 4.5, greeting: 'Hey!');
}

Output:

4.5
Hey!

final list = [1, 2, 3];
final [a, b, c] = list;
print('$a $b $c');

Output:

1 2 3

What if, we need more variable for more value
or we need to skip some value. Below is the code for both cases...

final list = [1, 2, 3, 4, 5, 6, 7, 8, 9];
final [a, b, c, ...d] = list;
print('$a $b $c $d');

Output

1 2 3 [4, 5, 6, 7, 8, 9]

final list = [1, 2, 3, 4, 5, 6, 7, 8, 9];
final [a, _, c, ...d] = list;
print('$a $c $d');

Here b is skipped.
Output:

1 3 [4, 5, 6, 7, 8, 9]

With class related stuff.

void main() {
  final human = Human('Nice Name', 2);
  final Human(:name, :age) = human;
  print(name);
  print(age);
}

class Human {
  final String name;
  final int age;
  Human(this.name, this.age);
}

Output:

Nice Name
2

List<String> listItems = ['HI', 'man'];
switch (listItems) {
  case ['Hi' || 'HI', 'man' || 'MAN']:
    print('matched');
}

Output:

matched