type UserId = string
type PostId = string

function getUser(id: UserId) { /* ... */ }

const postId: PostId = "post-123"
getUser(postId) // No error! Both are just `string`

// brand.ts
declare const __brand: unique symbol
type Brand<T, B extends string> = T & { readonly [__brand]: B }

import type { Brand } from './brand'

type UserId = Brand<string, 'UserId'>
type PostId = Brand<string, 'PostId'>
type Email  = Brand<string, 'Email'>

type Meters       = Brand<number, 'Meters'>
type Seconds      = Brand<number, 'Seconds'>
type PositiveInt  = Brand<number, 'PositiveInt'>

function getUser(id: UserId) { /* ... */ }

const postId = "post-123" as PostId
getUser(postId) // TS Error: PostId is not assignable to UserId

function createUserId(id: string): UserId {
  if (!id || id.length === 0) throw new Error('Invalid UserId')
  return id as UserId
}

function validateEmail(input: string): Email {
  if (!/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(input)) {
    throw new Error('Invalid email')
  }
  return input as Email
}

function toPositiveInt(n: number): PositiveInt {
  if (!Number.isInteger(n) || n <= 0) throw new Error('Must be positive integer')
  return n as PositiveInt
}

type UserId    = Brand<string, 'UserId'>
type PostId    = Brand<string, 'PostId'>
type CommentId = Brand<string, 'CommentId'>

function getPost(postId: PostId) { /* ... */ }
function deleteComment(commentId: CommentId) { /* ... */ }

type Email           = Brand<string, 'Email'>
type NonEmptyString  = Brand<string, 'NonEmptyString'>
type SanitizedHTML   = Brand<string, 'SanitizedHTML'>
type TranslationKey  = Brand<string, 'TranslationKey'>

type Meters       = Brand<number, 'Meters'>
type Feet         = Brand<number, 'Feet'>
type Seconds      = Brand<number, 'Seconds'>
type Milliseconds = Brand<number, 'Milliseconds'>
type Percentage   = Brand<number, 'Percentage'> // 0-100

type AccessToken  = Brand<string, 'AccessToken'>
type RefreshToken = Brand<string, 'RefreshToken'>
type ApiKey       = Brand<string, 'ApiKey'>

// WRONG — __brand does not exist at runtime
if ((value as any).__brand === 'UserId') { /* ... */ }

// BAD — no validation, defeats the purpose
const userId = someString as UserId

// GOOD — validated constructor
const userId = createUserId(someString)

// file-a.ts — Brand<string, 'Id'>
// file-b.ts — Brand<number, 'Id'>
// These share the brand name 'Id' but mean different things!

import { z } from 'zod'

const UserIdSchema = z.string().uuid().brand<'UserId'>()
type UserId = z.infer<typeof UserIdSchema> // string & Brand<'UserId'>

const parsed = UserIdSchema.parse(input) // typed as UserId

import { text } from 'drizzle-orm/pg-core'

// Brand the column output type
const users = pgTable('users', {
  id: text('id').primaryKey().$type<UserId>(),
})

// Queries return UserId, not plain string
const user = await db.select().from(users).where(eq(users.id, userId))