关于高阶组件的问题
```ts
import React from 'react';

function Hello() {
    return <p>Hello</p>
}

interface Loading {
    loading: boolean
}

function HelloHOC<P>(WrappedComponent: React.ComponentType<P>) {
    return class extends React.Component<P extends Loading> {
        render() {
            const { loading, ...props } = this.props;
            return loading ? <p>loading</p> : <WrappedComponent {...props as P}/>
        }
    }
}


export default HelloHOC(Hello);
```

为什么不能使用 P extends Loading 而是 P & Loading