Question

I'm trying to 'denormalize' two arrays (IObservableArray and IObservableArray) where array A has objects with id's that point to id's of objects in array B. I would like to put objects from array B that match the id of the object in array A on object A as a dynamically named property. The arrays are IObservableArrays from mobx but that should not be of importance.

I'm trying to achieve this:

var aArr: IObservableArray<A extends { bId: number }>;
var bArr: IObservableArray<B extends { id: number }>;

var d = denormalize(aArr, bArr, (a, b) => a.bId === b.id, "b");
console.log(d[0].b) // => B

I tried the following:

export function denormalize<A, B, K extends string, TRet extends A & {[asProperty: K]: B}>(
    arr1: IObservableArray<A>,
    arr2: IObservableArray<B>,
    where: (a: A, b: B) => boolean,
    asProperty: K
): IObservableArray<TRet> {
    return observable.array(); // stub
}

But it says [ts] An index signature parameter type must be 'string' or 'number'. (parameter) k: K extends string

Is there a way to make the A[asProperty]: B work so that the compiler knows that the type returned by denormalize has an additional property with name asProperty and it autocompletes as such?

Answer 1

您不能在索引签名中使用泛型类型，索引器参数必须为string或number（这取决于spec）。

您可以使用映射类型语法（[Prop in Key] : Type）

export function denormalize<A, B, K extends string, TRet extends A & { [P in K]: B}>(
    arr1: IObservableArray<A>,
    arr2: IObservableArray<B>,
    where: (a: A, b: B) => boolean,
    asProperty: K
): IObservableArray<TRet> {
    // ...
}

会工作：

console.log(d[0].b) // => B

修改

正如@jcalz在评论中提到的，签名也可以使用与Record<K extends string, T>相同的{ [P in K]: B}>类型。使用此签名将是：

export function denormalize<A, B, K extends string, TRet extends A &  Record<K,B>>(
    arr1: IObservableArray<A>,
    arr2: IObservableArray<B>,
    where: (a: A, b: B) => boolean,
    asProperty: K
): IObservableArray<TRet>

非规范化数组<a> and Array<b> where clause is true, set B as named property on A

1 个答案: