trait & impl for typescript

trait.ts

type ImplType<I, M, O> = I & ThisType<I & M & {owner: O}>
type ImplFor<X, O = never> = <I, M = X>(trait: ImplType<I, M, O>) => (model: M, owner?: O) => I & M & {owner: O}

// simple but slow
const MutableImpl = <I, M, O>(trait: ImplType<I, M, O>) =>
  (model: M, owner?: O) => 
  Object.setPrototypeOf(model, Object.assign(trait, {owner}))

// better performance
const CopyImpl = <I, M extends Record<string, unknown>, O>(impl: ImplType<I, M, O>) => (model: M, owner?: O) => {
  const pdesc: PropertyDescriptorMap = {}
  Object.entries(model).forEach(([k, value])=>{ pdesc[k] = {value, writable: true, enumerable: true}})
  pdesc['owner'] = {value: owner, writable: false, enumerable: false}
  return Object.create(impl, pdesc);
}
const ImplFor = CopyImpl

// types
type User = {name: string, age: number}
type Group = {id: string, users: User[]}

// impl for User
const userImplGen: ImplFor<User, Group> = ImplFor
const userImpl = userImplGen({
  getName(){ return this.name },
  addAge(){ this._test += this.age },
  _test: 0,
  get test() { return this._test },
  usersCount() { return this.owner.users.length }
})
type UserImpl = ReturnType<typeof userImpl>

// impl for Group
const groupImplGen: ImplFor<Group> = ImplFor
const groupImpl = groupImplGen({
  get userModels(){ return this.users.map((x: User)=>userImpl(x, this))}
})

// data
const user: User = {name: 'namae', age: 17}
const group: Group = {id: 'test', users: [user]}

// binding
const groupModel = groupImpl(group)
console.log(groupModel.users)
console.log(groupModel.userModels[0].usersCount())

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAkgtmANgFXBAPDANFAsjgeQD4oBeWKAMimQAsBLAZ1Ukyr3YG8B7AdwDsIAJwBcUAgF8iAKFCRYCRADFuQ9AA1CZKIIBuwkuUw5c29UQAUwIQEN6wMfCQsM2PISIBKMiQtxuACYQiGL4UHyCQgD8YgTepCQw7KbUPALCsRLS0gD0OVCM9IrQAEYArsAFiHzSAMbc-IyVuBU2JYgQTojaxu7iltZ2DgrOaL1hxPEyUFB+gcGhOBHCMeJTUNIzBCUAVhC1wAB0jBDAAApC3MBXaAQAZnNBiIS7+0c2jIUA5vxWtvY4NKRCSeTzZPJQEqnYDCKCQIR3VRwGz8WoQOoNJpQADC3DAIC6PTcpggAA8YfwAowoAAlfaqALoJpCej8L44Mr8ADW-AiRA8FiKSEcihc4w860eCz6y2isXWnE2UHqjUqYCCjFqYgueOEoAAIhBNSywNchLgbGBtJwsltXgdDhB+NZ6EapYhPIdEUIAKI2Wq0CwWADaXJwuhsiDKEAAup4Epw4RraqGY9aI1GIDheCzgG0OmJrNGcE6ynBhPmIIWhNGJCCleqjSmAOSy5tp8icDPRsSy7O5ytiO6Rk4l-hlivtKtQYeIE62qBCU5lIT8cT2o61Jc2GGCxQ4RuazwAbmkWRVWK6KiE2lx+K64PyciNsjQUAAqicb53+DZy2JmVZdkoBsL5p3HOAoSELJnygABxS4yitTt6ACACXTZDkv0YMRP2EYMYyyXJ8iFbpvQ-L8MVVKAyi-Lo4KdEUkGvdA8KEHAEO4JDDBGZRVCorFaOEQlyCEoR6KdCxFRmMDgAAOT-CALE8RMl2AFc12ABhGEOX9yygCQsCVGwAgCABBMDlMTLSmEOAB9GEsQAanIGydNA6BDKVByjWGAAGIyZNOKBHOAZSoFU5dVxC7T7NCgzApo7DcU5MLvEi9Torcw5ZUOMSdI6NktIMs8wVgtiRNpKL+DFZ9uDuJLhMUGRiKgUiZ1UeDELAATKi+bqJP4Ji+LUTjuO0K9+IvPqBsUbR+q4sBBqkpVZMa815jnKzF2qmLbPyw5kTAINSVwr94yIMSugsUkcDc0EsnrVqAh3GxevWs7YR-RSxGbPSbAgZscA8sQAEYAHZz0xGbFrEMbkIi1DftCoH1pwqBgzEwjH0hVkAiA96FqQ3BNvm2akAsImwDBC9uA6Q5qi+SnupJp48uwmnMTpiAGe4JmqdZ4J2eEQW52DPyY2FoRGBS51lLBIA

なんで owner 作るのにこだわったのか忘れた