ℹ️ This repository is part of my Refactoring catalog based on Fowler's book with the same title. Please see kaiosilveira/refactoring for more details.

---

Hide delegate

Before	After
manager = aPerson.department.manager;	manager = aPerson.manager; class Person { get manager() { return this._department.manager; } // ... }

Inverse of: Remove middle man

Encapsulation is at the roots of good code design, it helps in keeping coupling low by hiding the internal details of a given class/module, which allows for better and safer refactorings, freedom for exploring new ideas (which eventually leads to deeper, more supple domain models). This refactoring sheds some light on how to hide our delegates, therefore keeping our data encapsulated.

Working example

Our working example is simple and straightforward: we have a Person class that contains some department info. The info related to a person's manager is inside the department reference, but that'd be great if we could hide the implementation details from the clients.

Test suite

A supporting test suite was added to make sure none of our refactoring steps introduced any errors. It covers the client code resolving the manager info of a given person.

describe('getManager', () => {
  it('should fetch the manager of a person', () => {
    const department = new Department();
    department.chargeCode = '123';
    department.manager = 'Martin';

    const aPerson = new Person({ name: 'Kaio' });
    aPerson.department = department;

    expect(getManager(aPerson)).toEqual('Martin');
  });
});

Steps

We start by adding a manager getter to Person:

diff --git a/src/Person.js b/src/Person.js
@@ -14,5 +14,8 @@
export class Person {
   set department(arg) {
     this._department = arg;
   }
-}

+  get manager() {
+    return this._department.manager;
+  }
+}

Then, we can simply update our callers to read the manager info directly from Person instead of accessing its department:

diff --git a/src/client/index.js b/src/client/index.js
@@ -1,4 +1,4 @@
 export function getManager(aPerson) {
-  const manager = aPerson.department.manager;
+  const manager = aPerson.manager;
   return manager;
 }

And that's it, as simple as that! In a real-world scenario, though, this could be a gradual process where we update caller by caller at a varying pace. The code would remain functional until we eventually finish updating all callers and remove the department getter completely:

diff --git a/src/Person.js b/src/Person.js
@@ -7,10 +7,6 @@
export class Person {
     return this._name;
   }

-  get department() {
-    return this._department;
-  }
-
   set department(arg) {
     this._department = arg;
   }

Commit history

Below there's the commit history for the steps detailed above.

Commit SHA	Message
872871b	add a get to manager at Person
d1c4386	update Person clients to read manager prop directly from it
a4f2280	remove department getter at Person

For the full commit history for this project, check the Commit History tab.