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Custom Enums (A | B)

There's two different types of enums - enums and unions.

TypeScript enums​

A TypeScript enum is essentially just an object where each key is backed by ascending integer values. Nitrogen will generate a C++ enum natively, which bridges to JS as a simple integer:

import { type HybridObject, iOS } from 'nitro-core'

enum Gender {
  MALE,
  FEMALE
}
@iOS(...)
export declare class Person extends HybridObject {
  getGender(): Gender
}

This is efficient because MALE is the number 0, FEMALE is the number 1, and all other values are invalid.

TypeScript union​

A TypeScript union is essentially just a variant of literal strings, which is only "typed" via TypeScript.

import { type HybridObject, iOS } from 'nitro-core'

type Gender = 'male' | 'female'
@iOS(...)
export declare class Person extends HybridObject {
  getGender(): Gender
}

Nitrogen statically generates hashes for the strings "male" and "female" at compile-time, allowing for very efficient conversions between JS strings and native enums.

Unions need a name​

A TypeScript union consisting of only literal strings needs to be aliased to a separate type so that nitrogen can generate the native enum accordingly.

Bad ❌
import { type HybridObject, iOS } from 'nitro-core'


@iOS(...)
export declare class Person extends HybridObject {
  getGender(): 'male' | 'female'
}
Good ✅
import { type HybridObject, iOS } from 'nitro-core'

type Gender = 'male' | 'female'
@iOS(...)
export declare class Person extends HybridObject {
  getGender(): Gender
}