creating template variable contexts

context.directive.ts

import { Directive, Input, ViewContainerRef, TemplateRef, EmbeddedViewRef } from '@angular/core';

@Directive({selector: '[context]'})
export class ContextDirective {

  private view: EmbeddedViewRef<any>;

  @Input() set contextFrom(context) {
    if (!this.view) {
      this.view = this.viewContainer.createEmbeddedView(this.template);
    }
    this.view.context.$implicit = context;
  }

  constructor(private viewContainer: ViewContainerRef, private template: TemplateRef<any>) {}

}

Example of case: avoid multiple observer subscriptions with async pipes everywhere.

Got the inspiration for it here: https://www.youtube.com/watch?v=ZqGvilzDbac&feature=youtu.be&t=46m6s