factoryize-example.js

import { Inject, Directive } from 'decorators';

@Inject('$scope', '$compile')
@Directive('myDirective')
class MyDirective {
  constructor($scope, $compile) {
    // ...
  }
}

// Step 1: factoryize is called with MyDirective
const factory = factoryize(MyDirective)

// Step 2: There are dependencies, so we end up calling Inject by
// unpacking the $inject array. factoryize becomes:
const factory = Inject('$scope', '$compile')((...dependencies) => new MyDirective(...dependencies))

// Step 3: Consider the second parameter to Inject, this is our 
// anonymous factory. When Angular passes in the dependencies, we
// treat is as an array and unpack it into the directive constructor.
const factory = Inject('$scope', '$compile')(($scope, $compile) => new MyDirective($scope, $compile))