Is there a way to implement Rust's enum variant classes or Kotlin sealed classes in TypeScript?

Question

Is there a way to implement Rust's enum variant classes or Kotlin sealed classes in TypeScript?

When working with HTTP responses in TypeScript, I am interested in creating a variant type that can represent different states. In Rust, a similar type can be defined as:

enum Response<T> {
    Empty,
    Loading,
    Failure(String),
    Success(data: T),
}

In Kotlin, sealed classes can achieve the same concept:

sealed class Response<out: T> {
  object Empty: Response<Nothing>()
  object Loading: Response<Nothing>()
  class Failure(val err: string): Response<Nothing>()
  class Success(val data: T): Response<T>
}

I wonder if there is a way to implement this variant type structure in TypeScript?

typescript typescript-generics

Answer 1

Answer №1

Special thanks to @gabriele-petrioli for suggesting the use of a discriminated union.

type EmptyState = {
  kind: "empty";
};

type LoadingState = {
  kind: "loading"
};

type ErrorState = {
  kind: "error"
  message: string;
};

type SuccessState<T> = {
  kind: "success"
  data: T;
};

type RequestState<T> =
  | EmptyState
  | LoadingState
  | ErrorState
  | SuccessState<T>;

function process<T>(response: RequestState<T>) {
  switch (response.kind) {
    case "error":
      response.message;
      break;
    case "success":
      response.data;
  }
}

Answer 2

Special thanks to @gabriele-petrioli for suggesting the use of a discriminated union.

type EmptyState = {
  kind: "empty";
};

type LoadingState = {
  kind: "loading"
};

type ErrorState = {
  kind: "error"
  message: string;
};

type SuccessState<T> = {
  kind: "success"
  data: T;
};

type RequestState<T> =
  | EmptyState
  | LoadingState
  | ErrorState
  | SuccessState<T>;

function process<T>(response: RequestState<T>) {
  switch (response.kind) {
    case "error":
      response.message;
      break;
    case "success":
      response.data;
  }
}

Answer 3

Answer №2

Below is a versatile type that automatically builds the union.

Additionally, I've included a convenient intoEnum function for simplified usage.

type PartialRustEnum<K extends string, V> = {
    kind: K
} & {
    [P in K]: V
}

export type RustEnum<T> = {
    [K in keyof T & string]: PartialRustEnum<K, T[K]>;
}[keyof T & string]

export function intoEnum<K extends string, V>(kind: K, value: V): PartialRustEnum<K, V> {
    return { kind, [kind]: value } as any
}

Example of usage:

type FooOrBar = RustEnum<{
    foo: number
    bar: string
}>

let a: FooOrBar = intoEnum('foo',32)

if(a.kind === 'foo'){
  // recognized as foo
  console.log(a.foo)
}else{
  // recognized as bar
  console.log(a.bar)
}

Answer 4

Below is a versatile type that automatically builds the union.

Additionally, I've included a convenient intoEnum function for simplified usage.

type PartialRustEnum<K extends string, V> = {
    kind: K
} & {
    [P in K]: V
}

export type RustEnum<T> = {
    [K in keyof T & string]: PartialRustEnum<K, T[K]>;
}[keyof T & string]

export function intoEnum<K extends string, V>(kind: K, value: V): PartialRustEnum<K, V> {
    return { kind, [kind]: value } as any
}

Example of usage:

type FooOrBar = RustEnum<{
    foo: number
    bar: string
}>

let a: FooOrBar = intoEnum('foo',32)

if(a.kind === 'foo'){
  // recognized as foo
  console.log(a.foo)
}else{
  // recognized as bar
  console.log(a.bar)
}

Is there a way to implement Rust's enum variant classes or Kotlin sealed classes in TypeScript?

Answer №1

Answer №2

Similar questions

What steps should I take to ensure my paths in Ionic 4 Typescript are functioning properly?

Understanding the Purpose of the Pipe Function in Angular 2 and Typescript Observables

The updated values in an Angular application may not always be accurately represented by interpolated values

Tips for showcasing styled text in Vue using API data

I am looking to develop a unique event that can be triggered by any component and listened to by any other component within my Angular 7 application

Having trouble retrieving spot price using Uniswap SDK due to a transaction error LOK

The dropdown cannot be disabled because it is being passed as an input parameter

Eliminate private TypeScript class properties from an object by using Vue 3's ref and reactive features

From milliseconds to hours: a straightforward conversion

What is the best method for combining two observables into one?

Adding a total property at the row level in JavaScript

When there is data present in tsconfig.json, Visual Studio Code does not display errors inline for TypeScript

Is it possible to execute methods in the initialization phase using Express Route?

Creating a modal dialog using a function in a TypeScript file

In the world of mathematics, the equation 1+1 may actually equal 11 instead

An error message occurs in TypeScript when trying to access a property that does not exist in an array

Provide a string argument when instantiating an abstract class

"Organize your files with React and TypeScript using a file list

The existence of useRef.current is conditional upon its scope, and it may be null in certain

Determining in Angular 8 whether a value has been altered by a user or by a method call