Anonymous Functions and Lambda Expressions

In Dart, anonymous functions (also known as lambda expressions or function literals) are functions that don't have a name. These functions are used when a short, self-contained function is needed temporarily, such as when passing a function as an argument to another function.

Defining Anonymous Functions

An anonymous function is defined like a normal function but without a name.

Syntax-

(parameterList) {

// Function body

};

Lambda Expressions (Short-Hand Syntax)

A lambda (or arrow function) is a shorter syntax for an anonymous function. It's used when the function has a single expression.

The syntax uses => instead of {}.

Syntax-

(parameterList) => expression;

Examples of Anonymous Functions

1. Assigning to a Variable

You can assign an anonymous function to a variable and call it later.

void main() {

var printMessage = (String message) {

print("Message: $message");

};

printMessage("Hello, Dart!"); // Output: Message: Hello, Dart!

}

2. Passing to a Higher-Order Function

Anonymous functions are often passed to higher-order functions like forEach or map.

void main() {

var numbers = [1, 2, 3, 4];

numbers.forEach((number) {

print("Number: $number");

});

}

Examples of Lambda Expressions

1. Assigning a Lambda to a Variable

You can use the shorthand syntax to create concise one-line functions.

void main() {

var square = (int number) => number * number;

print(square(4)); // Output: 16

}

2. Using with a Higher-Order Function

Lambdas are especially useful for one-liners passed to higher-order functions.

void main() {

var numbers = [1, 2, 3, 4];

// Using lambda inside forEach

numbers.forEach((number) => print("Number: $number"));

// Using lambda with map

var squaredNumbers = numbers.map((number) => number * number).toList();

print(squaredNumbers); // Output: [1, 4, 9, 16]

}

When to Use Anonymous Functions or Lambdas

Anonymous functions: When the logic requires multiple statements or conditions.
Lambdas: When the function is a simple one-liner.

Examples

1. Assigning an Anonymous Function to a Variable

void main() {

var greet = (String name) {

print("Hello, $name!");

};

greet("Alice"); // Output: Hello, Alice!

}

2. A Lambda Expression to Calculate Square

void main() {

var square = (int number) => number * number;

print(square(4)); // Output: 16

}

3. Passing Anonymous Functions to forEach

void main() {

var names = ["Alice", "Bob", "Charlie"];

names.forEach((name) {

print("Name: $name");

});

}

4. Using a Lambda with map

void main() {

var numbers = [1, 2, 3];

var doubled = numbers.map((n) => n * 2).toList();

print(doubled); // Output: [2, 4, 6]

}

5. Filtering a List Using Lambda

void main() {

var numbers = [1, 2, 3, 4];

var evens = numbers.where((n) => n.isEven).toList();

print(evens); // Output: [2, 4]

}

6. Summing Numbers Using reduce

void main() {

var numbers = [1, 2, 3];

var sum = numbers.reduce((a, b) => a + b);

print(sum); // Output: 6

}

7. Conditional Print with Anonymous Function

void main() {

var printIfEven = (int number) {

if (number.isEven) print("Even: $number");

};

printIfEven(4); // Output: Even: 4

printIfEven(5); // No output

}

8. Returning Functions Using Lambda

Function multiplier(int factor) => (int number) => number * factor;

void main() {

var triple = multiplier(3);

print(triple(4)); // Output: 12

}

9. Anonymous Function for Sorting

void main() {

var fruits = ["apple", "banana", "cherry"];

fruits.sort((a, b) => b.compareTo(a));

print(fruits); // Output: [cherry, banana, apple]

}

10. Lambda with fold

void main() {

var numbers = [1, 2, 3];

var product = numbers.fold(1, (prev, element) => prev * element);

print(product); // Output: 6

}

11. Using a Lambda to Check Conditions

void main() {

var isEven = (int n) => n % 2 == 0;

print(isEven(4)); // Output: true

print(isEven(5)); // Output: false

}

12. Combining Multiple Lambdas

void main() {

var add = (int a, int b) => a + b;

var multiply = (int a, int b) => a * b;

print(add(2, 3)); // Output: 5

print(multiply(2, 3)); // Output: 6

}

13. Anonymous Function in Timer

import 'dart:async';

void main() {

Timer(Duration(seconds: 2), () {

print("Timer executed!");

});

}

14. Using Lambda in Custom Transform

List<int> transform(List<int> numbers, int Function(int) operation) {

return numbers.map(operation).toList();

}

void main() {

var numbers = [1, 2, 3];

var doubled = transform(numbers, (n) => n * 2);

print(doubled); // Output: [2, 4, 6]

}

15. Nested Anonymous Functions

void main() {

var calculate = (int x) {

return (int y) => x + y;

};

var addFive = calculate(5);

print(addFive(3)); // Output: 8

}

16. Lambda with any

void main() {

var numbers = [1, 2, 3];

var hasEven = numbers.any((n) => n.isEven);

print(hasEven); // Output: true

}

17. Lambda with every

void main() {

var numbers = [2, 4, 6];

var allEven = numbers.every((n) => n.isEven);

print(allEven); // Output: true

}

18. Filtering Names with Anonymous Functions

void main() {

var names = ["Alice", "Bob", "Charlie"];

var filtered = names.where((name) => name.startsWith("A")).toList();

print(filtered); // Output: [Alice]

}

19. Using Anonymous Function in a Custom Filter

List<int> filter(List<int> numbers, bool Function(int) condition) {

return numbers.where(condition).toList();

}

void main() {

var result = filter([1, 2, 3, 4], (n) => n > 2);

print(result); // Output: [3, 4]

}

20. Lambda Expression for String Manipulation

void main() {

var formatString = (String input) => "Formatted: ${input.toUpperCase()}";

print(formatString("hello")); // Output: Formatted: HELLO

}

Program 10: Working with Functions

void main() {

// Function declaration

int add(int a, int b) {

return a + b;

}

// Function call

int result = add(5, 3);

print('Result: $result');

// Anonymous function

var multiply = (int a, int b) => a * b;

print('Multiply: ${multiply(4, 5)}');

}

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