在多个NgModules (特别是monorepo，Nrwl Nx风格)中提供可重用单例服务的最佳实践

// shared.module.ts
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';

import { SharedService } from './shared.service';
import { SharedModuleComponent } from './shared-component.component';
import { SharedModuleDirective } from './shared-directive.directive';
import { SharedModulePipe } from './shared-pipe.pipe';

@NgModule({
  imports: [
    CommonModule
  ],
  declarations: [
    SharedModuleComponent,
    SharedModuleDirective,
    SharedModulePipe
  ],
  providers: [
    SharedService
  ],
  exports: [
    SharedModuleComponent,
    SharedModuleDirective,
    SharedModulePipe
  ]
})
export class SharedModule { }

// app.module.ts
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';

import { SharedModule } from './shared/shared.module';
import { AppComponent } from './app.component';

@NgModule({
  imports: [
    BrowserModule,
    SharedModule
  ],
  declarations: [
    AppComponent
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

// feature.module.ts
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';

import { SharedModule } from '../shared/shared.module';
import { FeatureComponent } from './feature.component';

@NgModule({
  imports: [
    CommonModule,
    SharedModule
  ],
  declarations: [
    FeatureComponent
  ]
})
export class FeatureModule { }