What is the difference between named and positional parameters in Dart?

In the Dart language, function parameters can be specified in two ways: named parameters and positional parameters. The primary distinction lies in how values are passed during function calls and how they enhance code readability and flexibility.

Positional Parameters

• Definition: Positional parameters pass values based on their order in the function definition.
• Required: Unless marked as optional, all positional parameters must be provided in the defined order during function calls.
• Optional: Optional positional parameters can be defined by enclosing them in square brackets [] within the parameter list.

Example:

dart
void sayHello(String firstName, String lastName, [String title]) {
  var result = 'Hello, ';
  if (title != null) {
    result += '$title ';
  }
  result += '$firstName $lastName';
  print(result);
}

// Call
sayHello('Jane', 'Doe');                  // Output: Hello, Jane Doe
sayHello('Jane', 'Doe', 'Dr.');           // Output: Hello, Dr. Jane Doe

Named Parameters

• Definition: Named parameters pass values through parameter names, independent of position.
• Required: By default, all named parameters are optional unless explicitly marked as required.
• Optional: Named parameters are defined using curly braces {} and can include default values.

Example:

dart
void createContact({String firstName, String lastName, String email}) {
  print('Creating contact $firstName $lastName with email $email');
}

// Call
createContact(firstName: 'John', lastName: 'Doe', email: 'john.doe@example.com');
createContact(firstName: 'John', email: 'john.doe@example.com');  // lastName can be omitted

Summary:

• Positional parameters are ideal for functions with few parameters where order is intuitive or when calls should remain minimalist.
• Named parameters offer greater flexibility and readability, especially with many parameters or inconsistent importance. They allow focusing only on necessary parameters while omitting others.
• When designing function interfaces, selecting the appropriate parameter type significantly impacts code clarity and usability.