Set operations

Learn Set management with add, contains and remove.

Set operations

You add to a Set with add, remove with remove, and ask membership with contains. For example fruits.add('cherry'); places a new value in the Set.

contains returns a boolean: fruits.contains('apple') gives true when 'apple' is in the Set. remove drops the item; if it is not there, it does nothing silently.

The length property tells you how many items the Set holds; isEmpty and isNotEmpty are handy for quick checks. A Set offers no indexed access; reach for a List when order matters.

contains and remove

contains asks whether a value lives in the Set. For example fruits.contains('banana') returns false when 'banana' is absent. This is much faster than a list's indexOf.

remove throws the given value out of the Set. fruits.remove('apple') deletes 'apple'; if it is missing, no error is raised. The return value is a boolean: true if removed, false otherwise.

Together these three methods keep a Set alive: add to place, contains to check, remove to clean.

Exercise Three friends list

Create a Set<String>. Use add to insert three friend names, then use contains to print whether the name 'Ayşe' is in the Set.

Show example solution

void main() {
  var friends = <String>{};
  friends.add('Mert');
  friends.add('Deniz');
  friends.add('Cem');
  print(friends.contains('Ayşe'));
}

Test yourself

The add call

void main() {
  var fruits = <String>{'apple'};
  fruits.____('pear');
  print(fruits);
}

Show answer

void main() {
  var fruits = <String>{'apple'};
  fruits.add('pear');
  print(fruits);
}

What does contains return?
```
var fruits = <String>{'apple'};
print(fruits.contains('banana'));
```
- void
- String
- bool (true/false)
- int
Show answer

bool (true/false) — bool. contains answers the membership question with true or false.
Match the operations

add

Inserts an element
contains

Tests membership
remove

Drops an element
length

Element count

Next lesson: Map

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