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dynamic

Learn the dynamic type and runtime type checking.

The dynamic type

dynamic is a flexible type that can hold any value. When you make a variable dynamic, Dart leaves type checks to runtime.

For example dynamic x = 5; then x = 'text'; is valid. Because dynamic accepts any type.

This flexibility is not risk-free: type errors only appear when the program runs. So use dynamic carefully; prefer var or explicit types when possible.

The is operator

The is operator checks what type a variable has at runtime. x is int returns true if x is an int.

It is especially used with dynamic variables; their type is not known in advance. You check with is first, then use it safely.

Example: dynamic x = 5; if (x is int) { print('integer'); }. This gives runtime type safety.

Practice dynamic and is

Declare dynamic x = 5;. Check with if (x is int) and print print('int').

Starter code

main.dart
// Use dynamic and is

Sample solution

main.dart
void main() {
  dynamic x = 5;
  if (x is int) {
    print('int');
  }
}

Expected output

int

Questions and answers

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

1 Flexible type

Question 
____ x = 5;
Answer 
dynamic x = 5;

Explanation: dynamic accepts every type.

2 What is the difference between dynamic and var?

  • They are exactly the same
  • dynamic is faster
  • var is safer
  • in dynamic the type can change later Correct answer

Explanation: In dynamic the type can change at runtime; in var it cannot.

3 dynamic concepts

Term Meaning
dynamic Flexible type
is Type check
var Inference
int Integer

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