Iteration Podcast

Encapsulation

Jun 24 '19

Episode 6 - More Code Examples

Drawing from Chapter 7 - Encapsulation

A weekly podcast about programming, development, and design through the lens of amazing books, chapter-by-chapter.

Encapsulate Record (162)

var organization = { name: "JP Sio", country: "USA" };

becomes ⬇️

class Organization {
  constructor(data) {
    this._name = data.name;
    this._country = data.country;
  }

  get name() {
    return this._name;
  }
  set name(arg) {
    this._name = arg;
  }

  get country() {
    return this._country;
  }
  set country(arg) {
    this._country = arg;
  }
}

you can hide what is stored and provide methods
consumer of class Organization doesn't need to know / care which is stored and which is calculated
nice getter and setter methods
makes it easier to refactor -> can hide implementation of internals and update the internals while keeping the same external interface

Encapsulate Collection (170)

class Person {
  get courses() {
    return this._courses;
  }
  set courses(aList) {
    this._courses = aList;
  }
}

becomes ⬇️

class Person {
  get courses() {
    return this._courses.slice();
  }
  addCourse(aCourse) {
    /*...*/
  }
}

slice() is key here, does not modify the original array - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice
common approach is to provide a getting method for the collection to return a copy
basically, never mutate the original

Replace Primative with Object (174)

orders.filter(0 => "high" === o.priority || "rush" === o.priority)

becomes ⬇️

orders.filter(o => o.priority.higherThan(new Priority("normal")));

this goes back to "Primitive Obsession"

programmers are often hesitant to create their own types and rely only on primitives. i.e. representing a phone number as a string instead of as it's own type

A telephone number may be represented as a string for a while, but later it will need special behavior for formatting, extracting the area code, and the like

create a new class for that bit of data
at first, the class does very little. in fact it probably only wraps a primitive
but now you have a place to put behavior specific to its needs

Inline Function (115) 🥴

Sometimes it's better to not try to split things apart, sometimes it just complicates things.

// before refactor: 

function getItemPrice(item) {
  if (itemOnSale(item) == true) {
    return item.price - 5
  } else {
    return item.price
  }
};

function itemOnSale(product) {
  if (product.onSale == true) {
    return true;
  } else {
    return false;
  }
};

let original = getItemPrice(sweatshirt);

// after refactor: 

function newGetItemPrice(item) {
  if (item.onSale == true) {
    return item.price - 5
  } else {
    return item.price
  }
};

Extract Class (182) 🥴

Talk through HUGE applicant model (in Ruby)
Broke this into child objects
- Applicant Health History
- Applicant Habits
- Applicant Lifestyle
- Applicant Method
- Applicant Legal Release