For Each

In the following Dart Program, we apply forEach method for a list, a set and a map.

1. List:



void main() {

  var nums = [1, 2, 3, 4, 5, 6, 7];

  nums.forEach((element) {

    element *= 11;

    print(element);

  });

  print(nums);

}





11
22
33
44
55
66
77
[1, 2, 3, 4, 5, 6, 7]




2. Set:



void main() {

  var eng = {"one", "two", "three", "four", "five"};

  var fr = ["un", "deux", "trois", "quatre", "cinq"];

  var engAndFr = eng;

  var index = 0;

  engAndFr.forEach((element) {

    element = element + " " + fr[index];

    index++;

    print(element);

  });

  print(engAndFr);

}





one un
two deux
three trois
four quatre
five cinq
{one, two, three, four, five}




3. Map



void main() {

  String carDescription = "My car is";

  var car = {

    "model": "R8",

    "Horsepower": "602",

    "Energy": "Gasoline",

    "transmission": "automatic"

  };

  car.forEach((key, value) {

    carDescription += " " + value;

  });

  

  print(carDescription);

}





My car is R8 602 Gasoline automatic





You may ask a questio here : Why forEach is unable to modify the elements of the list and the set ?




The element parameter of the forEach callback is just a normal local variable, and assigning to it has no effect outside the callback.

Why ?

Dart does not have variable references, all elements are passed as a reference to an object, not to a variable. (In other words, Dart is purely "call-by-sharing" like both Java and JavaScript).
The same goes for iterators: they return the value in the iterable, but it has no reference back to the iterable after that.

     Source