源代码位置：
export interface MemoizedSelector<State, Result, ProjectorFn = DefaultProjectorFn<Result>> extends Selector<State, Result> { release(): void; projector: ProjectorFn; setResult: (result?: Result) => void; clearResult: () => void; }
MemoizedSelector包含两部分属性：
extends Selector
Selector的定义：一个函数，输入参数类型为State，返回参数类型为Result，
因此，MemorizedSelector，首先它也是一个函数。
在函数的基础上，MemoizedSelector多了下面四个属性：
通过Object.assign, 将函数本身同 extends区块里定义的4个属性进行merge：
export declare type DefaultProjectorFn<T> = (...args: any[]) => T;
同普通函数相比，DefaultProjectorFn的特点在于，限定了返回类型的类型为T, 在消费该类型时，必须指定该类型。
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}));
