vue3-core/packages/reactivity/src/ref.ts

import { track, trigger } from './effect'
import { TrackOpTypes, TriggerOpTypes } from './operations'
import { isObject } from '@vue/shared'
import { reactive, isReactive } from './reactive'
import { ComputedRef } from './computed'
import { CollectionTypes } from './collectionHandlers'

const isRefSymbol = Symbol()

export interface Ref<T = any> {
  // This field is necessary to allow TS to differentiate a Ref from a plain
  // object that happens to have a "value" field.
  // However, checking a symbol on an arbitrary object is much slower than
  // checking a plain property, so we use a _isRef plain property for isRef()
  // check in the actual implementation.
  // The reason for not just declaring _isRef in the interface is because we
  // don't want this internal field to leak into userland autocompletion -
  // a private symbol, on the other hand, achieves just that.
  [isRefSymbol]: true
  value: T
}

const convert = <T extends unknown>(val: T): T =>
  isObject(val) ? reactive(val) : val

export function isRef<T>(r: Ref<T> | unknown): r is Ref<T>
export function isRef(r: any): r is Ref {
  return r ? r._isRef === true : false
}

export function ref<T>(value: T): T extends Ref ? T : Ref<UnwrapRef<T>>
export function ref<T = any>(): Ref<T | undefined>
export function ref(value?: unknown) {
  return createRef(value)
}

export function shallowRef<T>(value: T): T extends Ref ? T : Ref<T>
export function shallowRef<T = any>(): Ref<T | undefined>
export function shallowRef(value?: unknown) {
  return createRef(value, true)
}

function createRef(value: unknown, shallow = false) {
  if (isRef(value)) {
    return value
  }
  if (!shallow) {
    value = convert(value)
  }
  const r = {
    _isRef: true,
    get value() {
      track(r, TrackOpTypes.GET, 'value')
      return value
    },
    set value(newVal) {
      value = shallow ? newVal : convert(newVal)
      trigger(
        r,
        TriggerOpTypes.SET,
        'value',
        __DEV__ ? { newValue: newVal } : void 0
      )
    }
  }
  return r
}

export function unref<T>(ref: T): T extends Ref<infer V> ? V : T {
  return isRef(ref) ? (ref.value as any) : ref
}

export type CustomRefFactory<T> = (
  track: () => void,
  trigger: () => void
) => {
  get: () => T
  set: (value: T) => void
}

export function customRef<T>(factory: CustomRefFactory<T>): Ref<T> {
  const { get, set } = factory(
    () => track(r, TrackOpTypes.GET, 'value'),
    () => trigger(r, TriggerOpTypes.SET, 'value')
  )
  const r = {
    _isRef: true,
    get value() {
      return get()
    },
    set value(v) {
      set(v)
    }
  }
  return r as any
}

export function toRefs<T extends object>(
  object: T
): { [K in keyof T]: Ref<T[K]> } {
  if (__DEV__ && !isReactive(object)) {
    console.warn(`toRefs() expects a reactive object but received a plain one.`)
  }
  const ret: any = {}
  for (const key in object) {
    ret[key] = toProxyRef(object, key)
  }
  return ret
}

function toProxyRef<T extends object, K extends keyof T>(
  object: T,
  key: K
): Ref<T[K]> {
  return {
    _isRef: true,
    get value(): any {
      return object[key]
    },
    set value(newVal) {
      object[key] = newVal
    }
  } as any
}

// corner case when use narrows type
// Ex. type RelativePath = string & { __brand: unknown }
// RelativePath extends object -> true
type BaseTypes = string | number | boolean | Node | Window

// Recursively unwraps nested value bindings.
export type UnwrapRef<T> = {
  cRef: T extends ComputedRef<infer V> ? UnwrapRef<V> : T
  ref: T extends Ref<infer V> ? UnwrapRef<V> : T
  array: T
  object: { [K in keyof T]: UnwrapRef<T[K]> }
}[T extends ComputedRef<any>
  ? 'cRef'
  : T extends Array<any>
    ? 'array'
    : T extends Ref | Function | CollectionTypes | BaseTypes
      ? 'ref' // bail out on types that shouldn't be unwrapped
      : T extends object ? 'object' : 'ref']