The document discusses refactoring code to improve its structure and design. It provides examples of code with conditional logic based on an object's type. The examples show moving this conditional logic into subclass methods to better distribute the responsibilities. This polymorphic approach removes the need for conditionals and centralizes the logic with each object type. The author also shares references for further reading on refactoring techniques and code smells.

2. Cork Software Crafters

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4. Paulo Clavijo @pclavijo

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Paulo Clavijo @pclavijo

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Paulo Clavijo @pclavijo

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Paulo Clavijo @pclavijo

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Paulo Clavijo @pclavijo

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23. Paulo Clavijo @pclavijo

24. Paulo Clavijo @pclavijo
More of …
- Good names
- SOLID code
- Value objects
- Pure functions
...
Less of …
- Duplicate code
- Long Method
- Data Clumps
- Message Chains
...

25. Paulo Clavijo @pclavijo

26. Paulo Clavijo @pclavijo
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27. Paulo Clavijo @pclavijo
class Login {
private ContactInfo contactInfo;
public boolean authenticate(String userName, String password) {
// logic to validate that password:
// is at least 8 characters long
// contains a capital letter, a lowercase, a number …
…
// logic to verify if password matches user password
…
}

28. Paulo Clavijo @pclavijo
class User {
private ContactInfo contactInfo;
public User(ContactInfo contactInfo) {
this.contactInfo = contactInfo;
}
public String getFullAddress() {
String fullAddress = contactInfo.getStreetName() + " " +
contactInfo.getStreetNumber() + ", " +
contactInfo.getZipCode() + ", " +
contactInfo.getCity() + ", " +
contactInfo.getCountry();
return fullAddress;
}

29. Paulo Clavijo @pclavijo
class Invoice {
private Customer customer;
public Invoice(Customer customer) {
this.customer = customer;
}
public double getShippingCost() {
if (customer.getAddress().getCountry().isInEurope())
return STANDARD_SHIPPING_COST;
else
return OUTSIDE_EU_SHIPPING_COST;
}
...
}

30. Paulo Clavijo @pclavijo

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37. Paulo Clavijo @pclavijo
function getPayAmount() {
if (isDead) return deadAmount();
if (isSeparated) return separatedAmount();
if (isRetired) return retiredAmount();
return normalPayAmount();
}
function getPayAmount() {
let result;
if (isDead)
result = deadAmount();
else {
if (isSeparated)
result = separatedAmount();
else {
if (isRetired)
result = retiredAmount();
else
result = normalPayAmount();
}
}
return result;
}

38. Paulo Clavijo @pclavijo
if (summer())
charge = summerCharge();
else
charge = regularCharge();
if (!aDate.isBefore(plan.summerStart) && !aDate.isAfter(plan.summerEnd))
charge = quantity * plan.summerRate;
else
charge = quantity * plan.regularRate + plan.regularServiceCharge;

39. Paulo Clavijo @pclavijo
orders.filter(o => o.priority.higherThan(new Priority("normal")));
orders.filter(o => "high" === o.priority ||
"rush" === o.priority);

40. Paulo Clavijo @pclavijo
function amountInvoiced(aDateRange) {...}
function amountReceived(aDateRange) {...}
function amountOverdue(aDateRange) {...}
function amountInvoiced(startDate, endDate) {...}
function amountReceived(startDate, endDate) {...}
function amountOverdue(startDate, endDate) {...}

41. Paulo Clavijo @pclavijo
class Scorer {
constructor(candidate, medicalExam, scoringGuide) {
this._candidate = candidate;
this._medicalExam = medicalExam;
this._scoringGuide = scoringGuide;
}
execute() {
this._result = 0;
this._healthLevel = 0;
// long body code
}
}
function score(candidate, medicalExam, scoringGuide) {
let result = 0;
let healthLevel = 0;
// long body code
}

42. Paulo Clavijo @pclavijo
function setHeight(value) { this._height = value; }
function setWidth (value) { this._width = value; }
function setDimension(name, value) {
if (name === "height") {
this._height = value;
return;
}
if (name === "width") {
this._width = value;
return;
}
}

43. Paulo Clavijo @pclavijo
function totalOutstanding() {
return customer.invoices
.reduce((total, each) => each.amount + total, 0);
}
function sendBill() {
emailGateway.send(formatBill(customer));
}
function getTotalOutstandingAndSendBill() {
const result = customer.invoices
.reduce((total, each) => each.amount + total, 0);
sendBill();
return result;
}

44. Paulo Clavijo @pclavijo
const names = input
.filter(i => i.job === "programmer")
.map(i => i.name);
const names = [];
for (const i of input) {
if (i.job === "programmer")
names.push(i.name);
}

45. Paulo Clavijo @pclavijo
class EuropeanSwallow {
get plumage() { return 'average'; }
}
class AfricanSwallow {
get plumage() { return (this.numberOfCoconuts > 2) ? 'tired' : 'average'; }
}
class NorwegianBlueParrot {
get plumage() { return (this.voltage > 100) ? 'scorched' : 'beautiful'; }
}
switch (bird.type) {
case 'EuropeanSwallow':
return "average";
case 'AfricanSwallow':
return (bird.numberOfCoconuts > 2) ? "tired" : "average";
case 'NorwegianBlueParrot':
return (bird.voltage > 100) ? "scorched" : "beautiful";
default:
return "unknown";
}

46. Paulo Clavijo @pclavijo
function createEmployee(name, type) {
switch (type) {
case "engineer":
return new Engineer(name);
case "salesman":
return new Salesman(name);
case "manager":
return new Manager(name);
}
}
function createEmployee(name, type) {
return new Employee(name, type);
}

47. Paulo Clavijo @pclavijo
class UnknownCustomer {
get name() {return 'occupant';}
}
if (aCustomer === 'unknown') customerName = 'occupant';

48. Paulo Clavijo @pclavijo
const orderRecord = parseOrder(order);
const orderPrice = price(orderRecord, priceList);
function parseOrder(aString) {
const values = aString.split(/s+/);
return ({
productID: values[0].split("-")[1],
quantity: parseInt(values[1]),
});
}
function price(order, priceList) {
return order.quantity * priceList[order.productID];
}
const orderData = orderString.split(/s+/);
const productPrice = priceList[orderData[0].split("-")[1]];
const orderPrice = parseInt(orderData[1]) * productPrice;

49. Paulo Clavijo @pclavijo
leadEngineer = createEngineer(document.leadEngineer);
leadEngineer = new Employee(document.leadEngineer, 'E');

50. Paulo Clavijo @pclavijo

52. https://github.com/emilybache/Parrot-Refactoring-Kata

53. Paulo Clavijo @pclavijo
class EuropeanSwallow {
get plumage() { return 'average'; }
}
class AfricanSwallow {
get plumage() { return (this.numberOfCoconuts > 2) ? 'tired' : 'average'; }
}
class NorwegianBlueParrot {
get plumage() { return (this.voltage > 100) ? 'scorched' : 'beautiful'; }
}
switch (bird.type) {
case 'EuropeanSwallow':
return "average";
case 'AfricanSwallow':
return (bird.numberOfCoconuts > 2) ? "tired" : "average";
case 'NorwegianBlueParrot':
return (bird.voltage > 100) ? "scorched" : "beautiful";
default:
return "unknown";
}

54. Problem
Solution
You have a conditional that chooses different behaviors
depending on the type of an object.
Move each leg of the conditional to an overriding method
in a subclass. Make the original method abstract.

55. Mechanics
● If classes do not exist for polymorphic behavior, create them together
with a factory function to return the correct instance.
● Use the factory function in calling code.
● Move the conditional function to the superclass.
● If the conditional logic is not a self-contained function, use Extract
Function to make it so.
● Pick one of the subclasses. Create a subclass method that overrides the
conditional statement method. Copy the body of that leg of the
conditional statement into the subclass method and adjust it to fit.
● Repeat for each leg of the conditional.
● Leave a default case for the superclass method. Or, if superclass should
be abstract, declare that method as abstract or throw an error to show it
should be the responsibility of a subclass.

56. Paulo Clavijo @pclavijo

57. Paulo Clavijo @pclavijo

58. Paulo Clavijo @pclavijo

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Paulo Clavijo @pclavijo

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63. Paulo Clavijo @pclavijo

64. https://refactoring.com/catalog
http://sourcemaking.com/refactoring/smells
Paulo Clavijo @pclavijo
Digital Rights Management