ArkTS Specification

• 1. Introduction
  • 1.1. Common Description
  • 1.2. Lexical and Syntactic Notation
  • 1.3. Terms and Definitions
• 2. Lexical Elements
  • 2.1. Use of Unicode Characters
  • 2.2. Lexical Input Elements
  • 2.3. White Spaces
  • 2.4. Line Separators
  • 2.5. Tokens
  • 2.6. Identifiers
  • 2.7. Keywords
  • 2.8. Operators and Punctuators
  • 2.9. Literals
    • 2.9.1. Integer Literals
    • 2.9.2. Floating-Point Literals
    • 2.9.3. BigInt Literals
    • 2.9.4. Boolean Literals
    • 2.9.5. String Literals
    • 2.9.6. Template Literals
    • 2.9.7. Null Literal
    • 2.9.8. Undefined Literal
  • 2.10. Comments
  • 2.11. Semicolons
• 3. Types
  • 3.1. Predefined Types
  • 3.2. User-Defined Types
  • 3.3. Types by Category
  • 3.4. Using Types
  • 3.5. Named Types
  • 3.6. Type References
  • 3.7. Value Types
    • 3.7.1. Integer Types and Operations
    • 3.7.2. Floating-Point Types and Operations
    • 3.7.3. Numeric Types Hierarchy
    • 3.7.4. Boolean Types and Operations
  • 3.8. Reference Types
    • 3.8.1. Objects
    • 3.8.2. Object Class Type
    • 3.8.3. string Type
    • 3.8.4. never Type
    • 3.8.5. void Type
    • 3.8.6. Array Types
    • 3.8.7. Function Types
    • 3.8.8. null Type
    • 3.8.9. undefined Type
    • 3.8.10. Tuple Types
    • 3.8.11. Union Types
    • 3.8.12. Nullish Types
    • 3.8.13. DynamicObject Type
  • 3.9. Default Values for Types
• 4. Names, Declarations and Scopes
  • 4.1. Names
  • 4.2. Declarations
  • 4.3. Distinguishable Declarations
  • 4.4. Scopes
  • 4.5. Type Declarations
  • 4.6. Type Alias Declaration
    • 4.6.1. Recursive Type Aliases
  • 4.7. Variable and Constant Declarations
    • 4.7.1. Variable Declarations
    • 4.7.2. Constant Declarations
    • 4.7.3. Type Compatibility with Initializer
    • 4.7.4. Type Inference from Initializer
  • 4.8. Function Declarations
    • 4.8.1. Signatures
    • 4.8.2. Parameter List
    • 4.8.3. Readonly Parameters
    • 4.8.4. Optional Parameters
    • 4.8.5. Rest Parameter
    • 4.8.6. Shadowing Parameters
    • 4.8.7. Return Type
    • 4.8.8. Function Overload Signatures
• 5. Generics
  • 5.1. Generic Declarations
  • 5.2. Generic Parameters
  • 5.3. Type Parameter Constraint
  • 5.4. Generic Instantiations
  • 5.5. Type Parameter Default
  • 5.6. Type Arguments
  • 5.7. Utility Types
    • 5.7.1. Partial Utility Type
    • 5.7.2. Required Utility Type
    • 5.7.3. Readonly Utility Type
    • 5.7.4. Record Utility Type
• 6. Contexts and Conversions
  • 6.1. Assignment-like Contexts
  • 6.2. String Operator Contexts
  • 6.3. Numeric Operator Contexts
  • 6.4. Casting Contexts and Conversions
    • 6.4.1. Numeric Casting Conversions
    • 6.4.2. Narrowing Reference Casting Conversions
    • 6.4.3. Casting Conversions from Union
  • 6.5. Implicit Conversions
    • 6.5.1. Primitive Types Conversions
    • 6.5.2. Widening Primitive Conversions
    • 6.5.3. Constant Narrowing Integer Conversions
    • 6.5.4. Boxing Conversions
    • 6.5.5. Unboxing Conversions
    • 6.5.6. Widening Union Conversions
    • 6.5.7. Widening Reference Conversions
    • 6.5.8. Character to String Conversions
    • 6.5.9. Constant String to Character Conversions
    • 6.5.10. Function Types Conversions
    • 6.5.11. Enumeration to Int Conversions
    • 6.5.12. Enumeration to String Conversions
• 7. Expressions
  • 7.1. Evaluation of Expressions
    • 7.1.1. Normal and Abrupt Completion of Expression Evaluation
    • 7.1.2. Order of Expression Evaluation
    • 7.1.3. Operator Precedence
    • 7.1.4. Evaluation of Arguments
    • 7.1.5. Evaluation of Other Expressions
  • 7.2. Literal
  • 7.3. Qualified Name
  • 7.4. Array Literal
    • 7.4.1. Array Type Inference from Context
    • 7.4.2. Array Type Inference from Types of Elements
  • 7.5. Object Literal
    • 7.5.1. Object Literal of Class Type
    • 7.5.2. Object Literal of Interface Type
    • 7.5.3. Object Literal of Record Type
    • 7.5.4. Object Literal Evaluation
  • 7.6. Spread Expression
  • 7.7. Parenthesized Expression
  • 7.8. this Expression
  • 7.9. Field Access Expressions
    • 7.9.1. Accessing Current Object Fields
    • 7.9.2. Accessing Superclass Fields
  • 7.10. Method Call Expression
    • 7.10.1. Step 1: Selection of Type to Use
    • 7.10.2. Step 2: Selection of Method
    • 7.10.3. Step 3: Semantic Correctness Check
    • 7.10.4. Function or method selection
  • 7.11. Function Call Expression
    • 7.11.1. Step 1: Selection of Function
    • 7.11.2. Step 2: Semantic Correctness Check
  • 7.12. Indexing Expression
    • 7.12.1. Array Indexing Expression
    • 7.12.2. Record Indexing Expression
  • 7.13. Chaining Operator
  • 7.14. New Expressions
  • 7.15. Cast Expressions
  • 7.16. InstanceOf Expression
  • 7.17. TypeOf Expression
  • 7.18. Ensure-Not-Nullish Expression
  • 7.19. Nullish-Coalescing Expression
  • 7.20. Unary Expressions
    • 7.20.1. Postfix Increment
    • 7.20.2. Postfix Decrement
    • 7.20.3. Prefix Increment
    • 7.20.4. Prefix Decrement
    • 7.20.5. Unary Plus
    • 7.20.6. Unary Minus
    • 7.20.7. Bitwise Complement
    • 7.20.8. Logical Complement
  • 7.21. Multiplicative Expressions
    • 7.21.1. Multiplication
    • 7.21.2. Division
    • 7.21.3. Remainder
  • 7.22. Additive Expressions
    • 7.22.1. String Concatenation
    • 7.22.2. Additive Operators ‘+’ and ‘-’ for Numeric Types
  • 7.23. Shift Expressions
  • 7.24. Relational Expressions
    • 7.24.1. Numerical Comparison Operators <, <=, >, and >=
    • 7.24.2. String Comparison Operators <, <=, >, and >=
    • 7.24.3. Boolean Comparison Operators <, <=, >, and >=
  • 7.25. Equality Expressions
    • 7.25.1. Value Equality for Numeric Types
    • 7.25.2. Value Equality for Strings
    • 7.25.3. Value Equality for Booleans
    • 7.25.4. Value Equality for Characters
    • 7.25.5. Equality with null or undefined
    • 7.25.6. Reference Equality
  • 7.26. Bitwise and Logical Expressions
    • 7.26.1. Integer Bitwise Operators &, ^, and |
    • 7.26.2. Boolean Logical Operators &, ^, and |
  • 7.27. Conditional-And Expression
  • 7.28. Conditional-Or Expression
  • 7.29. Assignment
    • 7.29.1. Simple Assignment Operator
    • 7.29.2. Compound Assignment Operators
  • 7.30. Conditional Expressions
  • 7.31. String Interpolation Expressions
  • 7.32. Lambda Expressions
    • 7.32.1. Lambda Signature
    • 7.32.2. Lambda Body
    • 7.32.3. Lambda Expression Type
    • 7.32.4. Runtime Evaluation of Lambda Expressions
  • 7.33. Dynamic Import Expression
  • 7.34. Constant Expressions
• 8. Statements
  • 8.1. Normal and Abrupt Statement Execution
  • 8.2. Expression Statements
  • 8.3. Block
  • 8.4. Local Declarations
  • 8.5. if Statements
  • 8.6. loop Statements
  • 8.7. while Statements and do Statements
  • 8.8. for Statements
  • 8.9. for-of Statements
  • 8.10. break Statements
  • 8.11. continue Statements
  • 8.12. return Statements
  • 8.13. switch Statements
  • 8.14. throw Statements
  • 8.15. try Statements
    • 8.15.1. catch Clause
    • 8.15.2. finally Clause
    • 8.15.3. try Statement Execution
  • 8.16. Assert Statements
• 9. Classes
  • 9.1. Class Declarations
    • 9.1.1. Abstract Classes
    • 9.1.2. Final Classes
    • 9.1.3. Class Extension Clause
    • 9.1.4. Class Implementation Clause
    • 9.1.5. Implementing Interface Properties
  • 9.2. Class Body
  • 9.3. Class Members
  • 9.4. Access Modifiers
    • 9.4.1. Private Access Modifier
    • 9.4.2. Internal Access Modifier
    • 9.4.3. Protected Access Modifier
    • 9.4.4. Public Access Modifier
  • 9.5. Field Declarations
    • 9.5.1. Static Fields
    • 9.5.2. Readonly (Constant) Fields
    • 9.5.3. Field Initialization
  • 9.6. Method Declarations
    • 9.6.1. Class (Static) Methods
    • 9.6.2. Instance Methods
    • 9.6.3. Abstract Methods
    • 9.6.4. Final Methods
    • 9.6.5. Overriding Methods
    • 9.6.6. Native Methods
    • 9.6.7. Method Overload Signatures
    • 9.6.8. Method Body
    • 9.6.9. Inheritance
    • 9.6.10. Overriding by Instance Methods
    • 9.6.11. Hiding by Class Methods
    • 9.6.12. Requirements in Overriding and Hiding
    • 9.6.13. Inheriting Methods with Override-Equivalent Signatures
  • 9.7. Accessor Declarations
  • 9.8. Class Initializer
  • 9.9. Constructor Declaration
    • 9.9.1. Formal Parameters
    • 9.9.2. Constructor Overload Signatures
    • 9.9.3. Constructor Body
    • 9.9.4. Explicit Constructor Call
    • 9.9.5. Default Constructor
  • 9.10. Local Classes and Interfaces
• 10. Interfaces
  • 10.1. Interface Declarations
  • 10.2. Superinterfaces and Subinterfaces
  • 10.3. Interface Body
  • 10.4. Interface Members
  • 10.5. Interface Properties
  • 10.6. Interface Method Declarations
    • 10.6.1. Interface Method Overload Signatures
    • 10.6.2. Inheritance and Overriding
    • 10.6.3. Overriding by Instance Methods
    • 10.6.4. Overriding Requirements
    • 10.6.5. Interfaces Inheriting Methods with Override-Equivalent Signatures
• 11. Enumerations
  • 11.1. Enumeration Integer Values
  • 11.2. Enumeration String Values
  • 11.3. Enumeration Operations
• 12. Error Handling
  • 12.1. Errors
• 13. Compilation Units, Packages, and Modules
  • 13.1. Separate Modules
  • 13.2. Compilation Units in Host System
  • 13.3. Import Directives
    • 13.3.1. Bind All with Qualified Access
    • 13.3.2. Simple Name Binding
    • 13.3.3. Several Bindings for One Import Path
    • 13.3.4. Default Import Binding
    • 13.3.5. Type Binding
    • 13.3.6. Import Path
  • 13.4. Default Import
  • 13.5. Top-Level Declarations
    • 13.5.1. Exported Declarations
  • 13.6. Export Directives
    • 13.6.1. Selective Export Directive
    • 13.6.2. Export Type Directive
    • 13.6.3. Re-Export Directive
  • 13.7. Top-Level Statements
  • 13.8. Program Entry Point (main)
• 14. Ambient Declarations
  • 14.1. Ambient Variable Declarations
  • 14.2. Ambient Function Declarations
  • 14.3. Ambient Class Declarations
  • 14.4. Ambient Interface Declarations
  • 14.5. Ambient Namespace Declarations
• 15. Semantic Rules
  • 15.1. Subtyping
  • 15.2. Override-Equivalent Signatures
  • 15.3. Compatible Signature
  • 15.4. Overload Signature Compatibility
  • 15.5. Type Compatibility
  • 15.6. Compatibility Features
    • 15.6.1. Extended Conditional Expressions
• 16. Support for GUI Programming
  • 16.1. Annotations
  • 16.2. GUI Structs
  • 16.3. Builder Function Syntax Conventions
  • 16.4. Builder Function Restrictions
  • 16.5. Annotations List
    • 16.5.1. @Builder Annotation
    • 16.5.2. @BuilderParam Annotation
    • 16.5.3. @Component Annotation
    • 16.5.4. @Consume Annotation
    • 16.5.5. @Entry Annotation
    • 16.5.6. @Link Annotation
    • 16.5.7. @LocalStorageLink Annotation
    • 16.5.8. @LocalStorageProp Annotation
    • 16.5.9. @ObjectLink Annotation
    • 16.5.10. @Observed Annotation
    • 16.5.11. @Prop Annotation
    • 16.5.12. @Provide Annotation
    • 16.5.13. @State Annotation
    • 16.5.14. @StorageLink Annotation
    • 16.5.15. @StorageProp Annotation
    • 16.5.16. @Watch Annotation
  • 16.6. Callable Types
    • 16.6.1. Callable Types with Invoke Method
    • 16.6.2. Callable Types with Instantiate Method
  • 16.7. Additional Features
    • 16.7.1. Methods Returning this
    • 16.7.2. Unary operator ‘$$’
  • 16.8. Example of GUI Programming
• 17. Experimental Features
  • 17.1. Character Type and Literals
    • 17.1.1. Character Literals
    • 17.1.2. Character Type and Operations
  • 17.2. Array Creation Expressions
    • 17.2.1. Runtime Evaluation of Array Creation Expressions
  • 17.3. Indexable Types
  • 17.4. Iterable Types
  • 17.5. Statements
    • 17.5.1. For-of Type Annotation
    • 17.5.2. Multiple Catch Clauses in Try Statements
    • 17.5.3. Assert Statements
  • 17.6. Function and Method Overloading
    • 17.6.1. Function Overloading
    • 17.6.2. Class Method Overloading
    • 17.6.3. Interface Method Overloading
    • 17.6.4. Constructor Overloading
    • 17.6.5. Declaration Distinguishable by Signatures
  • 17.7. Native Functions and Methods
    • 17.7.1. Native Functions
    • 17.7.2. Native Methods
  • 17.8. Final Classes and Methods
    • 17.8.1. Final Classes
    • 17.8.2. Final Methods
  • 17.9. Default and Static Interface Methods
    • 17.9.1. Default Method Declarations
    • 17.9.2. Static Method Declarations
  • 17.10. Extension Functions
  • 17.11. Trailing Lambda
  • 17.12. Enumeration Super Type
    • 17.12.1. Enumeration Types Conversions
  • 17.13. Enumeration Methods
  • 17.14. Exceptions
    • 17.14.1. Throwing Functions
    • 17.14.2. Non-Throwing Functions
    • 17.14.3. Rethrowing Functions
    • 17.14.4. Exceptions and Initialization Expression
    • 17.14.5. Exceptions and Errors Inside Field Initializers
  • 17.15. Coroutines
    • 17.15.1. Create and Launch a Coroutine
    • 17.15.2. Awaiting a Coroutine
    • 17.15.3. The Promise<T> Class
    • 17.15.4. Structured Coroutines
    • 17.15.5. Channels Classes
    • 17.15.6. Async Functions
  • 17.16. Packages
    • 17.16.1. Internal Access Modifier
    • 17.16.2. Package Initializer
    • 17.16.3. Sub-Entity Binding
    • 17.16.4. All Static Sub-Entities Binding
    • 17.16.5. Import and Overloading of Function Names
    • 17.16.6. Overloading of Function Names
    • 17.16.7. Shadowing of Function Names
  • 17.17. Generics Experimental
    • 17.17.1. Declaration-Site Variance
    • 17.17.2. NonNullish Type Parameter
• 18. Standard Library
• 19. Grammar Summary
• 20. Implementation Details
  • 20.1. Import Path Lookup
  • 20.2. How to get type via reflection
• 21. ArkTS-TypeScript compatibility
  • 21.1. Undefined is Not a Universal Value
  • 21.2. Numeric Semantics
  • 21.3. Covariant Overriding
  • 21.4. Differences in Math.pow
• 22. Contributors