How to pass input variable in structure directive?

There is a structure directive:

 @Directive({
        selector: '[loading]',
    })
    export class LoadingDirective {
        loadingFactory: ComponentFactory<LoadingComponent>;
        loadingComponent: ComponentRef<LoadingComponent>;

        @Input()
        set loading(loading: boolean) {}
        @Input('loadingSize') size: number;
    
    }

I have tried to pass size:

<span *loading="true size=20"></span>