Sharing module with providers in Angular (i.e., https://alligator.io/angular/providers-shared-modules/)

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { CoreModule } from './core/core.module';

@NgModule({
  declarations: [],
  imports: [
    BrowserModule,
    CoreModule.forRoot()
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

core.module.ts

import { NgModule, ModuleWithProviders } from '@angular/core';
import { CommonModule } from '@angular/common';
import { SomeSharedService } from './shared.service';

@NgModule({
  imports: [
    CommonModule
  ],
  declarations: []
})
export class CoreModule {
  static forRoot(): ModuleWithProviders {
    return {
      ngModule: CoreModule,
      providers: [
        SomeSharedService
      ]
    };
  }
}

lazy-loaded.module.ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { CoreModule } from './../../core/core.module';
import { RouterModule } from '@angular/router';
import { SOME_ROUTES } from './some.routes';
import { SomeComponent } from './some-component/some.component';

@NgModule({
  imports: [
    CommonModule,
    CoreModule,
    RouterModule.forChild(SOME_ROUTES)
  ],
  declarations: [
    SomeComponent
  ]
})
export class LazyLoadedModule { }