Episode 2: Exploring Dart: Variables, Null Safety, Default Values, Late Variables, and Final & Const

Season 2: Exploring Dart #dartforbeginners

In the world of programming, Dart has carved a unique space for itself, and understanding its constructs can help you develop more efficient and safer apps. In this article, we're exploring five essential Dart concepts: Variables, Null Safety, Default Values, Late Variables, and Final & Const.

Dart Variables

In Dart, a variable is a storage location that holds a value. Variables store references to the data. For instance:

var name = 'Bob';

In this example, we've created a variable name and assigned it a string value 'Bob'. The variable name now refers to a String object containing the value 'Bob'.

It's possible to explicitly declare the type of a variable:

Object name = 'Bob';
String name = 'Bob';

In these examples, we've clarified that name is of type Object or String.

Null Safety in Dart

A standout feature of Dart is Null safety, a mechanism that helps prevent null dereference errors. These errors occur when you access a property or call a method on a null object. Null safety in Dart helps catch potential null errors during compile time.

You can specify a variable's nullability in Dart using the ? symbol:

String? name;  // Nullable
String name;   // Non-nullable

Appending ? to a type declares the variable as nullable, meaning it can contain a null value. Without the ?, the variable is non-nullable and must always hold a non-null value.

Default Values in Dart

In Dart, any uninitialized variable with a nullable type gets an initial value of null:

int? lineCount;
assert(lineCount == null);

In the example above, the variable lineCount has a default value of null because it's declared as nullable. For non-nullable variables, they must be initialized before using:

int lineCount = 0;

Here, lineCount is initialized with a zero value upon declaration.

Dart’s Late Variables

Dart introduces a keyword late that enables declaring a non-nullable variable to be initialized after its declaration. It also allows for lazily initializing a variable, i.e., initializing it the first time it's used.

late String description;

void main() {
  description = 'Feijoada!';
  print(description);
}

In the code above, we've used the late keyword, indicating to Dart that we will initialize the description variable at a later stage.

Final and Const in Dart

For variables that you don't want to change once set, Dart provides final and const keywords.

final name = 'Bob';
const bar = 1000000;

A final variable can only be set once and cannot be changed after it's been set. A const variable is for variables meant to be compile-time constants. All const variables are implicitly final.

Conclusion

Dart offers a rich and robust set of features for managing variables and their nullability. By preventing null errors, providing keywords for late initialization, and offering immutable variables via final and const, Dart ensures the safety and efficiency of your applications. A strong understanding of these concepts will considerably enhance your Dart coding skills. Keep exploring and happy coding!