Mis on põhjuseks, miks Dart 2.12 versioonis lisati märksõna abstract?

The abstract keyword in Dart 2.12 was introduced to explicitly denote abstract classes. Previously, abstract classes were defined implicitly, for example, if a class contained abstract methods (without implementation). The introduction of abstract allows:

• Explicitly marking a class as abstract, which improves code readability.
• Prohibiting direct instantiation of such classes.
• Improving support for static analysis and development tools.

Example of usage:

abstract class Animal {
  void makeSound(); // abstract method
}

class Dog extends Animal {
  @override
  void makeSound() {
    print('Bark');
  }
}

Here, Animal is an abstract class that cannot be instantiated directly.