Assign

题目来源(type-challenges)

问题 #

实现一个类型的 Object.assign

// case1
type Case1Target = {}

type Case1Origin1 = {
  a: 'a'
}

type Case1Origin2 = {
  b: 'b'
}

type Case1Origin3 = {
  c: 'c'
}

type Case1Answer = {
  a: 'a'
  b: 'b'
  c: 'c'
}

// case2
type Case2Target = {
  a: [1, 2, 3]
}

type Case2Origin1 = {
  a: {
    a1: 'a1'
  }
}

type Case2Origin2 = {
  b: [2, 3, 3]
}

type Case2Answer = {
  a: {
    a1: 'a1'
  }
  b: [2, 3, 3]
}

// case3

type Case3Target = {
  a: 1
  b: ['b']
}

type Case3Origin1 = {
  a: 2
  b: {
    b: 'b'
  }
  c: 'c1'
}

type Case3Origin2 = {
  a: 3
  c: 'c2'
  d: true
}

type Case3Answer = {
  a: 3
  b: {
    b: 'b'
  }
  c: 'c2'
  d: true
}

// case 4
type Case4Target = {
  a: 1
  b: ['b']
}

type Case4Answer = {
  a: 1
  b: ['b']
}

解答 #

type AssignObject<Target extends object, Source> = 
Source extends object
? {
  [K in keyof Target | keyof Source]: 
    K extends keyof Source 
    ? Source[K] 
    : K extends keyof Target 
    ? Target[K]: never
}
: Target

type Assign<T extends Record<string, unknown>, U extends unknown[]> = 
U extends [infer Head, ...infer Tail]
? Assign<AssignObject<T, Head>, Tail>
: T

拆分 #

• 递归合并
• Source 优先因为要覆盖原属性