forEach

Learn side-effect loops with forEach.

The forEach method

The forEach method performs an action for each element but returns nothing. It is used for side effects; for example printing each element.

Example: ['Apple', 'Banana', 'Cherry'].forEach((f) => print(f));. This prints each fruit on a separate line. Unlike map, forEach produces no result.

forEach replaces a loop. The code becomes shorter and more readable. But because it has no return value it cannot be chained.

forEach vs map

forEach and map look similar but serve different purposes. map returns a transformed collection; forEach returns nothing.

For side effects like printing use forEach. When you need transformed data use map. The wrong choice does not break the code but hurts readability.

Example: fruits.forEach((f) => print(f)); prints each fruit. fruits.map((f) => f.length) returns a list of lengths.

Exercise Print the fruits

Call forEach on the list ['Apple', 'Banana', 'Cherry']. Print each fruit with a 'Fruit: ' prefix; for example Fruit: Apple.

Show example solution

void main() {
  var fruits = ['Apple', 'Banana', 'Cherry'];
  fruits.forEach((f) => print('Fruit: $f'));
}

Test yourself

What does forEach return?
```
var a = [1, 2, 3].forEach((n) => print(n));
```
- A new list
- void (returns nothing)
- An Iterable
- A number
Show answer

void (returns nothing) — forEach returns nothing, it is void.
Match the forEach parts

(m) => print(m)

Side effect function
.forEach(...)

Call
void

Return type
print(m)

Print action

The forEach call

var fruits = ['Apple', 'Banana', 'Cherry'];
fruits.____((f) => print('Fruit: $f'));

Show answer

var fruits = ['Apple', 'Banana', 'Cherry'];
fruits.forEach((f) => print('Fruit: $f'));

Next lesson: any and every

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