function identity<T>(value: T): T {
  return value
}

interface ApiResponse<T> {
  code: number
  message: string
  data: T
}

type User = { name: string }

const res: ApiResponse<User> = {
  code: 200,
  message: "ok",
  data: { name: "Tom" }
}

type IsString<T> = T extends string ? true : false

type A = IsString<string> // true
type B = IsString<number> // false

type ElementType<T> = T extends (infer U)[] ? U : never

type A = ElementType<string[]> // string

type ReadOnly<T> = {
  readonly [K in keyof T]: T[K]
}

type User = {
  name: string
  age: number
}

type ReadonlyUser = ReadOnly<User>

type UserBasic = Pick<User, "name">

type UserWithoutAge = Omit<User, "age">

type PartialUser = Partial<User>

interface ApiResult<T> {
  code: number
  message: string
  data: T
}

async function request<T>(url: string): Promise<ApiResult<T>> {
  const res = await fetch(url)
  return res.json()
}

const user = await request<User>("/api/user")

const data: any = {}

type A<T, U, K, V> = ...