Utilize enums to implement a static member in a class

Question

Utilize enums to implement a static member in a class

Having this code snippet:

declare enum Snacks {
  APPLE = 'APPLE',
  CARROT = 'CARROT',
  JERKY = 'JERKY'
}

declare abstract class ForceSnacks {
  static snack : Snacks
}

export class MySnacks implements ForceSnacks {

  static snack = Snacks.APPLE;

}

Encountering an unfamiliar error:

https://i.sstatic.net/egTmy.png

Does anyone have a solution to resolve the ambient initializer error?

The error message reads as follows:

"Initializers are not allowed in ambient contexts"

Sometimes, another error appears:

"Ambient declaration should have no initializer"

typescript typescript2.0 typescript-2.5

Answer 1

Answer №1

As previously indicated in the comments, the code snippet you're referring to resides within a declaration file—specifically a `.d.ts` file. This is fitting considering the error message you've encountered. Declaration files are designed to contain ambient definitions (e.g. declare class MyFoods {}) as they primarily serve the purpose of outlining the type information of objects rather than providing their actual implementation.

It's worth noting that enforcing static properties, like the one you're trying to implement, isn't currently supported. However, there are alternative approaches available. One option is to utilize a singleton pattern, as demonstrated below:

// implemented in a .ts file
export enum Foods {
  CHERRY = 'CHERRY',
  LETTUCE = 'LETTUCE',
  JERKY = 'JERKY'
}

export interface ForceFoods {
  food: Foods;
}

export class MyFoods implements ForceFoods {
  private static _instance: MyFoods | undefined;

  food = Foods.CHERRY;

  private constructor() {
  }

  static get instance() {
    return this._instance || (this._instance = new MyFoods());
  }
}

// usage example...
MyFoods.instance.food;

Answer 2

As previously indicated in the comments, the code snippet you're referring to resides within a declaration file—specifically a `.d.ts` file. This is fitting considering the error message you've encountered. Declaration files are designed to contain ambient definitions (e.g. declare class MyFoods {}) as they primarily serve the purpose of outlining the type information of objects rather than providing their actual implementation.

It's worth noting that enforcing static properties, like the one you're trying to implement, isn't currently supported. However, there are alternative approaches available. One option is to utilize a singleton pattern, as demonstrated below:

// implemented in a .ts file
export enum Foods {
  CHERRY = 'CHERRY',
  LETTUCE = 'LETTUCE',
  JERKY = 'JERKY'
}

export interface ForceFoods {
  food: Foods;
}

export class MyFoods implements ForceFoods {
  private static _instance: MyFoods | undefined;

  food = Foods.CHERRY;

  private constructor() {
  }

  static get instance() {
    return this._instance || (this._instance = new MyFoods());
  }
}

// usage example...
MyFoods.instance.food;

Answer 3

Answer №2

declare enum Foods {
  APPLE = 'APPLE',
  CARROT = 'CARROT',
  BEEF = 'BEEF'
}

// class interface
interface ForceFoodsClass {
    food : Foods
    new (): ForceFoods;
}

// instance interface
interface ForceFoods {
    // just to show you will need to add a name property
    name: string;
}


export const MyFoods:ForceFoodsClass = class implements ForceFoods {

  static food = Foods.APPLE;
  name = "Apple delight"
}

Playground

Answer 4

declare enum Foods {
  APPLE = 'APPLE',
  CARROT = 'CARROT',
  BEEF = 'BEEF'
}

// class interface
interface ForceFoodsClass {
    food : Foods
    new (): ForceFoods;
}

// instance interface
interface ForceFoods {
    // just to show you will need to add a name property
    name: string;
}


export const MyFoods:ForceFoodsClass = class implements ForceFoods {

  static food = Foods.APPLE;
  name = "Apple delight"
}

Playground

Answer 5

Answer №3

The issue stemmed from having all the code contained within a declaration file (.d.ts). The solution is to move the implementing class to a .ts file:

// index.d.ts

export enum SCEPluginTypes {

  LANGUAGE = 'SCE_LANGUAGE'

}


declare enum Vegetables {
  CARROT = 'CARROT',
  SPINACH = 'SPINACH',
  BEET = 'BEET'
}


declare abstract class PowerVegetables {
  static vegetable : Vegetables
}

// index.ts

import {Vegetables, PowerVegetables} from "./index";

export class MyVegetables implements PowerVegetables {

  static vegetable = Vegetables.CARROT;

}

Answer 6

The issue stemmed from having all the code contained within a declaration file (.d.ts). The solution is to move the implementing class to a .ts file:

// index.d.ts

export enum SCEPluginTypes {

  LANGUAGE = 'SCE_LANGUAGE'

}


declare enum Vegetables {
  CARROT = 'CARROT',
  SPINACH = 'SPINACH',
  BEET = 'BEET'
}


declare abstract class PowerVegetables {
  static vegetable : Vegetables
}

// index.ts

import {Vegetables, PowerVegetables} from "./index";

export class MyVegetables implements PowerVegetables {

  static vegetable = Vegetables.CARROT;

}

Utilize enums to implement a static member in a class

Answer №1

Answer №2

Answer №3

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