Dart - Anonymous Functions

An anonymous function in Dart is like a named function but they do not have names associated with it. An anonymous function can have zero or more parameters with optional type annotations. An anonymous function consists of self-contained blocks of code and that can be passed around in our code as a function parameter.

• In Dart most of the functions are named functions we can also create nameless function knows as an anonymous function, lambda, or closure.
• In Dart, we can assign an anonymous function to constants or variables; later, we can access or retrieve the value of closure based on our requirements:

Syntax:

(parameter_list) {
       statement(s)
}

Anonymous Function in forEach()

Example: 

// Dartprogram to illustrate 
// Anonymous functions in Dart
void main()
{
    var list = ["Shubham","Nick","Adil","Puthal"];
    print("GeeksforGeeks - Anonymous function in Dart");
    list.forEach((item) {
        print('${list.indexOf(item)} : $item');
    });
}

Output:

GeeksforGeeks - Anonymous function in Dart
0 : Shubham
1 : Nick
2 : Adil
3 : Puthal

This example defines an anonymous function with an untyped parameter, item. The function, invoked for each item in the list, prints a string that includes the value at the specified index. 

Assigning an Anonymous Function to a Variable

In Dart, functions are treated as first-class objects, allowing us to assign an anonymous function to a variable and use it like a regular function.

Example:

void main() {
    // Assigning an anonymous function to a variable
    var multiply = (int a, int b) {
        return a * b;
    };
    
    print(multiply(5, 3)); // Output: 15
}

Output:

15

Using an Anonymous Function as a Callback

Anonymous functions are widely used in asynchronous operations like button clicks or API calls.

Example:

void performOperation(int a, int b, Function operation) {
    print('Result: ${operation(a, b)}');
}

void main() {
    // Passing an anonymous function
    performOperation(4, 2, (a, b) => a + b); 
}

Output:

Result: 6