Adaptation Rules from TypeScript to ArkTS (3)

ArkTS Constraints on TypeScript Features

Use class Instead of Types with Call Signatures

• Rule: arkts-no-call-signatures

• Severity: Error

• Description: ArkTS does not support call signatures in object types. Instead of using a type with a call signature, define a class with an invoke method.

• TypeScript Example:
  

type DescribableFunction = {
  description: string;
  (someArg: string): string; // call signature
};

function doSomething(fn: DescribableFunction): void {
  console.log(fn.description + " returned " + fn(""));
}

• ArkTS Example:

class DescribableFunction {
  description: string;

  constructor() {
    this.description = "desc";
  }

  public invoke(someArg: string): string {
    return someArg;
  }
}

function doSomething(fn: DescribableFunction): void {
  console.log(fn.description + " returned " + fn.invoke(""));
}

doSomething(new DescribableFunction());

Use class Instead of Types with Construct Signatures

• Rule: arkts-no-ctor-signatures-type

• Severity: Error

• Description: ArkTS does not support construct signatures in object types. Instead of using a type with a construct signature, define a class.

• TypeScript Example:
  

class SomeObject {}

type SomeConstructor = {
  new (s: string): SomeObject;
};

function fn(ctor: SomeConstructor) {
  return new ctor("hello");
}

• ArkTS Example:

class SomeObject {
  public f: string;

  constructor(s: string) {
    this.f = s;
  }
}

function fn(s: string): SomeObject {
  return new SomeObject(s);
}

Only One Static Block Allowed

• Rule: arkts-no-multiple-static-blocks

• Severity: Error

• Description: ArkTS does not allow multiple static blocks in a class. Merge multiple static blocks into a single one.

• TypeScript Example:
  

class C {
  static s: string;

  static {
    C.s = "aa";
  }

  static {
    C.s = C.s + "bb";
  }
}

• ArkTS Example:

class C {
  static s: string;

  static {
    C.s = "aa";
    C.s = C.s + "bb";
  }
}

No Support for Index Signatures

• Rule: arkts-no-indexed-signatures

• Severity: Error

• Description: ArkTS does not support index signatures. Use arrays instead.

• TypeScript Example:
  

interface StringArray {
  [index: number]: string;
}

function getStringArray(): StringArray {
  return ["a", "b", "c"];
}

const myArray: StringArray = getStringArray();
const secondItem = myArray[1];

• ArkTS Example:

class X {
  public f: string[] = [];
}

const myArray: X = new X();
myArray.f.push("a", "b", "c");
const secondItem = myArray.f[1];

Use Inheritance Instead of Intersection Types

• Rule: arkts-no-intersection-types

• Severity: Error

• Description: ArkTS does not support intersection types. Use inheritance instead.

• TypeScript Example:
  

interface Identity {
  id: number;
  name: string;
}

interface Contact {
  email: string;
  phoneNumber: string;
}

type Employee = Identity & Contact;

• ArkTS Example:

interface Identity {
  id: number;
  name: string;
}

interface Contact {
  email: string;
  phoneNumber: string;
}

interface Employee extends Identity, Contact {}

No Support for this Type

• Rule: arkts-no-typing-with-this

• Severity: Error

• Description: ArkTS does not support the this type. Use explicit concrete types instead.

• TypeScript Example:
  

interface ListItem {
  getHead(): this;
}

class C {
  n: number = 0;

  m(c: this) {
    // ...
  }
}

• ArkTS Example:

interface ListItem {
getHead(): ListItem;
}

class C {
n: number = 0;

m(c: C) {
// ...
}
}