Adaptation Rules from TypeScript to ArkTS (4)

ArkTS Constraints on TypeScript Features

No Support for Conditional Types

• Rule: arkts-no-conditional-types

• Severity: Error

  • Description: ArkTS does not support conditional type aliases. Introduce new types with explicit constraints or rewrite logic using Object.
  • TypeScript Example:

type X<T> = T extends number ? T : never;
type Y<T> = T extends Array<infer Item> ? Item : never;

• ArkTS Example:

// Provide explicit constraints in type aliases
type X1<T extends number> = T;

// Rewrite with Object, with less type control and a need for more type checks
type X2<T> = Object;

// Item must be used as a generic parameter and correctly instantiable
type YI<Item, T extends Array<Item>> = Item;

No Support for Field Declarations in Constructors

• Rule: arkts-no-ctor-prop-decls

• Severity: Error

  • Description: ArkTS does not support declaring class fields within constructors. Declare these fields within the class.
  • TypeScript Example:

class Person {
  constructor(
    protected ssn: string,
    private firstName: string,
    private lastName: string
  ) {
    this.ssn = ssn;
    this.firstName = firstName;
    this.lastName = lastName;
  }

  getFullName(): string {
    return this.firstName + ' ' + this.lastName;
  }
}

• ArkTS Example:

class Person {
  protected ssn: string;
  private firstName: string;
  private lastName: string;

  constructor(ssn: string, firstName: string, lastName: string) {
    this.ssn = ssn;
    this.firstName = firstName;
    this.lastName = lastName;
  }

  getFullName(): string {
    return this.firstName + ' ' + this.lastName;
  }
}

No Support for Constructor Signatures in Interfaces

• Rule: arkts-no-ctor-signatures-iface

• Severity: Error

  • Description: ArkTS does not support constructor signatures in interfaces. Use functions or methods instead.
  • TypeScript Example:

interface I {
  new (s: string): I;
}

function fn(i: I) {
  return new i('hello');
}

• ArkTS Example:

interface I {
  create(s: string): I;
}

function fn(i: I) {
  return i.create('hello');
}

No Support for Index Access Types

• Rule: arkts-no-aliases-by-index

• Severity: Error

  • Description: ArkTS does not support index access types.

No Support for Field Access by Index

• Rule: arkts-no-props-by-index

• Severity: Error

  • Description: ArkTS does not support dynamic field declaration or access. You can only access fields declared in the class or inherited visible fields. Accessing other fields will result in a compile - time error.
  • TypeScript Example:

class Point {
  x: string = '';
  y: string = '';
}
let p: Point = { x: '1', y: '2' };
console.log(p['x']);

class Person {
  name: string = '';
  age: number = 0;
  [key: string]: string | number;
}

let person: Person = {
  name: 'John',
  age: 30,
  email: '***@example.com',
  phoneNumber: '18*********',
};

• ArkTS Example:

class Point {
  x: string = '';
  y: string = '';
}
let p: Point = { x: '1', y: '2' };
console.log(p.x);

class Person {
  name: string;
  age: number;
  email: string;
  phoneNumber: string;

  constructor(name: string, age: number, email: string, phoneNumber: string) {
    this.name = name;
    this.age = age;
    this.email = email;
    this.phoneNumber = phoneNumber;
  }
}

let person = new Person('John', 30, '***@example.com', '18*********');
console.log(person['name']); // Compile - time error
console.log(person.unknownProperty); // Compile - time error

let arr = new Int32Array(1);
arr[0];