**Course Title:** Mastering Dart: From Fundamentals to Flutter Development **Section Title:** Functions and Error Handling **Topic:** Anonymous functions and arrow functions **Anonymous functions and arrow functions** ===================================================== In this topic, we will explore two important concepts in Dart: anonymous functions and arrow functions. These concepts are essential in functional programming and are used extensively in Flutter development. **What are Anonymous Functions?** --------------------------------- Anonymous functions, also known as lambda functions, are small, unnamed functions that can be defined inline within a larger expression. They are called "anonymous" because they are not declared with a name. Anonymous functions are useful when you need to pass a small, one-time use function as an argument to another function. **Declaring Anonymous Functions** ----------------------------- In Dart, you can declare an anonymous function using the following syntax: ```dart (type parameters) => expression; ``` Here's an example of an anonymous function that takes two integers and returns their sum: ```dart var sum = (int a, int b) => a + b; print(sum(10, 20)); // Outputs: 30 ``` In this example, we defined an anonymous function that takes two `int` parameters, `a` and `b`, and returns their sum. We then assigned this function to the `sum` variable. **Arrow Functions** ----------------- Arrow functions are a shorthand way of defining anonymous functions. They are used when the function body consists of a single expression. **Declaring Arrow Functions** --------------------------- In Dart, you can declare an arrow function using the following syntax: ```dart expression; ``` Here's an example of an arrow function that takes two integers and returns their sum: ```dart var sum = (int a, int b) => a + b; print(sum(10, 20)); // Outputs: 30 ``` Note that the syntax is the same as the anonymous function syntax. However, the key difference is that arrow functions can only contain a single expression. **Using Anonymous and Arrow Functions as Higher-Order Functions** ---------------------------------------------------------------- In functional programming, a higher-order function is a function that takes another function as an argument or returns a function as a result. Anonymous and arrow functions are often used as higher-order functions. Here's an example of using an anonymous function as a higher-order function: ```dart void printResult(int result, Function callback) { print('Result: $result'); callback(result); } void main() { var sum = (int a, int b) => a + b; printResult(sum(10, 20), (int result) => print('Callback result: $result')); } ``` In this example, we defined a higher-order function `printResult` that takes two arguments: `result` and `callback`. The `callback` argument is an anonymous function that takes an `int` parameter. **Using Anonymous and Arrow Functions as Event Handlers** --------------------------------------------------------- Anonymous and arrow functions can also be used as event handlers. For example, in Flutter, you can use an anonymous function as an event handler for a button press: ```dart ElevatedButton( child: Text('Click me'), onPressed: () => print('Button clicked'), ) ``` In this example, we defined an anonymous function that takes no arguments and prints a message to the console when the button is clicked. **Conclusion** ---------- In this topic, we explored the concepts of anonymous functions and arrow functions in Dart. We learned how to declare and use anonymous and arrow functions, and how to use them as higher-order functions and event handlers. **Practical Takeaways:** * Anonymous functions are small, unnamed functions that can be defined inline within a larger expression. * Arrow functions are a shorthand way of defining anonymous functions. * Anonymous and arrow functions can be used as higher-order functions and event handlers. * Use anonymous and arrow functions sparingly and only when necessary. **Example Use Cases:** * Using an anonymous function as a callback function in a network request. * Using an arrow function as an event handler for a button press. **Additional Resources:** * [Dart Language Tour](https://dart.dev/guides/language/language-tour): Learn more about anonymous and arrow functions in the official Dart language tour. * [Flutter Documentation](https://flutter.dev/docs/cookbook): Learn more about using anonymous and arrow functions in Flutter development. **Leave a Comment or Ask for Help:** If you have any questions or need help with this topic, please leave a comment below. Next Topic: [Error Handling using Try-Catch Blocks](next_topic)

(type parameters) => expression;

var sum = (int a, int b) => a + b;
print(sum(10, 20));  // Outputs: 30

expression;

var sum = (int a, int b) => a + b;
print(sum(10, 20));  // Outputs: 30

void printResult(int result, Function callback) {
  print('Result: $result');
  callback(result);
}

void main() {
  var sum = (int a, int b) => a + b;
  printResult(sum(10, 20), (int result) => print('Callback result: $result'));
}

ElevatedButton(
  child: Text('Click me'),
  onPressed: () => print('Button clicked'),
)