Encapsulation Made Simple

This post is greater than 300 words. I tried.

Encapsulation is often misunderstood as to just mean “a means of hiding data”. Encapsulation is really a tool for hiding how you operate on data.

What is encapsulation?

Let’s use an example. Say you have a contact with a name. You think the full name is a first and last name. So you write some code:

const getFullName = (firstName: string, lastName: string): string => `${firstName} ${lastName}`;

You use this function in many places across your app. You are asked to add prefix (e.g. Mr, Mrs) and suffix (e.g. Jr, Sr). You update the original function:

const getFullName = (firstName: string, lastName: string, prefix: string, suffix: string): string => `${prefix} ${firstName} ${lastName} ${suffix}`;

You are told that prefix and suffix are optional. Your code gets even more complicated:

const getFullName = (firstName: string, lastName: string, prefix?: string, suffix?: string): string => {
  let fullName = '';
  if (prefix) {
    fullName += `${prefix} `;
  }

  fullName += `${firstName} ${lastName}`;

  if (suffix) {
    fullName += ` ${suffix}`;
  }
  return fullName;
};

Now you want to show a prefix with just last name (e.g. Dr. Smith). You create another function to avoid adding parameters to the first function:

const getFormalName = (prefix: string, lastName: string): string => `${prefix} ${lastName}`;

You realize you sometimes need to append a . to the prefix. Middle names are now optional. You are asked to track maiden names. This name has become messy!

Thankfully, you can encapsulate all of this information.

class PersonName {
  constructor(
    private firstName: string,
    private lastName: string,
    private prefix?: string,
    private suffix?: string,
    private middleName?: string,
    private maidenName?: string,
  ) {}

  public getFormalName() {
    if (!this.prefix) {
      // Example fallback logic
      return this.lastName;
    }

    return `${this.prefix} ${this.lastName}`;
  }

  public getStandardName() {
    return `${this.firstName} ${this.lastName}`;
  }

  public getFullName() {
    let fullName = '';
    if (this.prefix) {
      fullName += `${this.prefix} `;
    }

    fullName += this.getStandardName();

    if (this.suffix) {
      fullName += ` ${this.suffix}`;
    }
    return fullName;
  }

  public getWithMaidenName() { /* logic */ }
}

Now you can just use PersonName to handle all of your name logic. Is is simple to add new functions that operate on names. You can make a change and the entire app reflects that change where PersonName is used.

Why is encapsulation hard?

It is hard because it can feel simpler to use data directly, but even minor changes in the requirements around that data can lead to an explosion of new code. If you have referenced a single function in multiple places across your app new requirements can result in serious refactoring.

It is also difficult to determine the correct amount of encapsulation. Understanding your data and how it is used is key. You wouldn’t need the abstraction above if you only reference first and last name one place in your application. As your system grows the need for encapsulation does, too.

Why use encapsulation?

You use it to share logic and to keep details of how you handle data private. What’s important is that you have a full name when you need one, not how it’s made. If tomorrow you need to remove prefix from the full name you can do it in a single place if you use proper encapsulation.

Encapsulation Made Simple

What is encapsulation and why would we need it?

What is encapsulation?

Why is encapsulation hard?

Why use encapsulation?

What can I learn next?

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