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LookUp

介绍​

过在联合类型Cat | Dog中通过指定公共属性type的值来获取相应的类型。换句话说，在以下示例中，LookUp<Dog | Cat, 'dog'>的结果应该是Dog，LookUp<Dog | Cat, 'cat'>的结果应该是Cat。

例如

ts
  
    interface Cat {
    type: 'cat'
    breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
  }
  interface Dog {
    type: 'dog'
    breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
    color: 'brown' | 'white' | 'black'
  }
  type MyDog = LookUp<Cat | Dog, 'dog'> // expected to be `Dog`
ts
  
    interface Cat {
    type: 'cat'
    breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
  }
  interface Dog {
    type: 'dog'
    breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
    color: 'brown' | 'white' | 'black'
  }
  type MyDog = LookUp<Cat | Dog, 'dog'> // expected to be `Dog`
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type LookUp<U, T> = any
 
/* _____________ Test Cases _____________ */
 
interface Cat {
  type: 'cat'
  breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
}
 
interface Dog {
  type: 'dog'
  breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
  color: 'brown' | 'white' | 'black'
}
 
type Animal = Cat | Dog
 
type cases = [
  Expect<Equal<LookUp<Animal, 'dog'>, Dog>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<LookUp<Animal, 'cat'>, Cat>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
ts
/* _____________ Your Code Here _____________ */
 
type LookUp<U, T> = any
 
/* _____________ Test Cases _____________ */
 
interface Cat {
  type: 'cat'
  breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
}
 
interface Dog {
  type: 'dog'
  breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
  color: 'brown' | 'white' | 'black'
}
 
type Animal = Cat | Dog
 
type cases = [
  Expect<Equal<LookUp<Animal, 'dog'>, Dog>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<LookUp<Animal, 'cat'>, Cat>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
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解决方案​

Spoiler warning // Click to reveal answer
ts
 
type LookUp<U, T> = U extends {type: T} ? U : never;
 
ts
 
type LookUp<U, T> = U extends {type: T} ? U : never;
 
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