Mastering Null-aware Operators in Dart: Safely Handling Null Values

Improve code safety and readability by efficiently dealing with null values in your Dart applications.

Learn how to effectively handle null values in Dart using null-aware operators, including 

• null-aware access (?.), 
• null-aware assignment (??=), 
• null-aware cascade (..), and 
• null-aware conditional (??). 

..

Null-aware access operator (?.): 

It is used to access properties or call methods on an object that may be null. If the object is null, the expression returns null without throwing an exception.

class Person {
  String name;
  Person(this.name);
  
  void sayHello() {
    print('Hello, $name!');
  }
}

void main() {
  Person? person; // Nullable Person object
  person?.sayHello(); // This will not throw an exception because of the null-aware access operator
}

..

Null-aware assignment operator (??=): 

This operator assigns a value to a variable only if the variable is currently null. It is a handy way to set default values for nullable variables.

void main() {
  int? num; // Nullable integer
  int defaultValue = 42;
  
  num ??= defaultValue; // Assigns the defaultValue to num only if num is null
  print(num); // Output: 42
  
  num ??= 10; // Since num is not null, it keeps the current value (42)
  print(num); // Output: 42
}

..

Null-aware cascade operator (..): 

It allows chaining multiple method calls on an object while ensuring the object is not null at each step. If the object is null, the cascade operation is skipped.

class Person {
  String name;
  Person(this.name);
  
  void sayHello() {
    print('Hello, $name!');
  }
  
  void introduce() {
    print('I am $name.');
  }
}

void main() {
  Person? person; // Nullable Person object
  
  person?.sayHello(); // This will not throw an exception because of the null-aware access operator
  person?.introduce(); // This will also not throw an exception because of the null-aware access operator
  
  // With the null-aware cascade operator, the chained method calls won't be executed if the object is null
  person?
    ..sayHello()
    ..introduce();
}

..

Null-aware conditional operator (??): 

This operator provides a default value when encountering a null value. It evaluates the expression on its left-hand side and returns it if it's non-null. Otherwise, it returns the expression on its right-hand side.

void main() {
  int? number; // Nullable integer
  int alternativeValue = 10;
  
  int result = number ?? alternativeValue; // If number is null, result will be assigned the value of alternativeValue
  print(result); // Output: 10
  
  number = 5; // Now number is not null
  result = number ?? alternativeValue; // Since number is not null, result will be assigned the value of number
  print(result); // Output: 5
}

..