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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.

Practice 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.

Starter code

main.dart
void main() {
  var friends = <String>{};
  // add three names

  // contains check for 'Ayşe' prints false
}

Sample solution

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

Expected output

false

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 The add call

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

Explanation: add appends a single element.

2 What does contains return?

main.dart
var fruits = <String>{'apple'};
print(fruits.contains('banana'));
  • void
  • String
  • bool (true/false) Correct answer
  • int

Explanation: bool. contains answers the membership question with true or false.

3 Match the operations

Term Meaning
add Inserts an element
contains Tests membership
remove Drops an element
length Element count

All lessons in Beginner

1 Dart basics

  1. What is Dart?
  2. Your first program
  3. dart run
  4. Comments
  5. String interpolation
  6. Summary - Dart basics

2 Variables

  1. var and type
  2. final
  3. const
  4. late
  5. Null safety
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and String
  4. Type inference
  5. dynamic
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Null-aware operators
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String interpolation
  3. length and methods
  4. substring
  5. contains and indexOf
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Pattern matching
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. for-in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Lists

  1. Creating lists
  2. List access
  3. add and remove
  4. length and contains
  5. List methods
  6. Summary - Lists

11 Sets and Maps

  1. Set
  2. Set operations
  3. Map
  4. Map operations
  5. Map iteration
  6. Summary - Sets and Maps

12 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Optional parameters
  5. First-class functions
  6. Summary - Functions

13 Null safety in depth

  1. Nullable types
  2. Null-aware operators
  3. The ! operator
  4. late
  5. Null check
  6. Summary - Null safety

14 Class basics

  1. class
  2. Constructor
  3. Instance variables
  4. Methods
  5. this
  6. Summary - Class basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. split and join
  2. replace
  3. trim and pad
  4. RegExp
  5. StringBuffer
  6. Summary - Advanced strings

17 Enums

  1. Defining enums
  2. Enum values
  3. Enhanced enums
  4. switch with enum
  5. Enum and patterns
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. The Exception class
  5. on clause
  6. Summary - Exceptions

19 Async basics

  1. Future
  2. async/await
  3. then
  4. Future.error
  5. Future.wait
  6. Summary - Async basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together