源代碼位置：

export interface MemoizedSelector<State, Result, ProjectorFn = DefaultProjectorFn<Result>> extends Selector<State, Result> {release(): void;projector: ProjectorFn;setResult: (result?: Result) => void;clearResult: () => void; }

MemoizedSelector包含兩部分屬性：

extends Selector<State,Result>

Selector的定義：一個函數，輸入參數類型為State，返回參數類型為Result，

因此，MemorizedSelector，首先它也是一個函數。

在函數的基礎上，MemoizedSelector多了下面四個屬性：

通過Object.assign, 將函數本身同 extends區塊里定義的4個屬性進行merge：

export declare type DefaultProjectorFn<T> = (...args: any[]) => T;

同普通函數相比，DefaultProjectorFn的特點在于，限定了返回類型的類型為T, 在消費該類型時，必須指定該類型。

export type AnyFn = (...args: any[]) => any;export type MemoizedProjection = {memoized: AnyFn;reset: () => void;setResult: (result?: any) => void;clearResult: () => void; }; export type MemoizeFn = (t: AnyFn) => MemoizedProjection; export type ComparatorFn = (a: any, b: any) => boolean; export type DefaultProjectorFn<T> = (...args: any[]) => T;export declare type Selector<T, V> = (state: T) => V;export interface MemoizedSelector<State, Result, ProjectorFn = DefaultProjectorFn<Result>> extends Selector<State, Result> {release(): void;projector: ProjectorFn;setResult: (result?: Result) => void;clearResult: () => void; }export interface JerryState {name: string,age: number }let jerryProjector = (data: string) => data.length;let jerryOriginFn = (data: JerryState) => data.name.length;let jerrySelector: MemoizedSelector<JerryState, number, DefaultProjectorFn<number>>;let oExtended = {release: () => {},projector: jerryProjector,setResult: (data: number) => {},clearResult: () => {} };jerrySelector = Object.assign(jerryOriginFn, oExtended);console.log('Ethan', jerrySelector({ name: 'Jerry', age: 31}));

更多Jerry的原創文章，盡在：“汪子熙”:

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