import { NgModule, Optional, SkipSelf } from '@angular/core';
import { CommonModule } from '@angular/common';

@NgModule({
  declarations: [],
  imports: [
    CommonModule
  ]
})
export class CoreModule { 
  constructor(@Optional() @SkipSelf() parentModule: CoreModule) {
    if(parentModule){
      throw new Error('CoreModule 只允许在 AppModule 中加载。');
    }
  }
}