In Dart, Each function has a name, Example function is main(), also called named functions.

How do you create a function without a name?

In dart, you create functions without a name, also called anonymous functions.

Anonymous functions contains zero or more arguments separated by comma and also have type annotations

anonymous functions also called lambda or closures in dart.

These functions can be assigned to variables or passed as an argument to functions.

Let’s see normal function define as below

String function getMessage(String message){
    return message;

}

The function can be called using with below syntax

getMessage("hello");

let’s see how the anonymous function

Dart closure or anonymous function example

Closure are special function also called lambda expression

Here is an example

(arguments)=>{
    return statement;
}

Arguments can be multiple arguments separated by a comma.

You can assign the closure functions to variables Let’s see anonymous function declaration Here is an example of nameless functions


void main() {
  // assign lambda function to variable
  var add = (int first, int second) => first + second;
  print(add(10, 20));
  
//  closure function without arrow syntax
  var add1 = (int first, int second) {
    return first + second;
  };
  print(add1(10, 20));
  
// closure function without assign variable
  (int first, int second) {
    print(first + second);
  }(10, 20);
  
}

How to pass closure function as a parameter in A function

printData function accepts two arguments, first int type, the second is Closure Function of type Function.

Here is an example program

void printData(int price, double Function(int amount) calculateFn) {
  var result = calculateFn(price);
  print(result);
}

void main() {
  var divideBy2 = (int price) {
    return price / 2; // return a double type.
  };
  var divideBy5 = (int price) {
    return price / 5; // return a double type.
  };
  const price = 50;
  printData(price, divideBy2); // 100.0
  printData(price, divideBy5); // 50.0
}

Dart closure or anonymous features

  • It has no function name
  • Arrow syntax used to create a closure
  • Can assign to variables or pass as an argument
  • If the body contains one expression, Return is an optional