1. Implementing The Open/Closed Principle

2. Sam Hennessy
• Originally from the UK
• Now live in Denver, CO
• Software Architect at i3logix
• Ex-Pro Services Consultant For Zend
• Regular at Front Range PHP Users Group
2

3. i3logix
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4. What is it?
Part of SOLID
Protect your system from change
Do you already do it?
4

5. SOLID
S Single responsibility
principle
O Open/closed principle
L Liskov substitution principle
I Interface segregation
principle
5
D Dependency inversion
principle

6. Open/Closed Principle
"Be open for extension,
but closed for
modification."
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7. And I Care Why?
Maintenance
Let your
Customer
users bridge a
customization
feature gap
Competitive Preventing
edge the "FORK"!
A-la-cart
feature
offerings
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8. What about YAGNI and KISS?
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9. Where Can It Be Applied?
Class
Application
Enterprise
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10. Classes

11. Classes
Inheritance
Polymorphism Interfaces
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12. Small Methods
12

13. No Public Properties
Always be private?
Encapsulation
Information hiding
It's cheap to do
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14. Globals and OCP
14

15. De-coupling
15

16. class Calculator{
public function __invoke($calc, $left, $right) {
if ($calc == 'add') {
return $left + $right;
} else if ($calc == 'sub') {
return $left - $right;
}
}
}

17. class Calculator{
public function __invoke(Calc $calc, $left, $right){
return $calc($left, $right);
}
}
$calculator = new Calculator();
echo $calculator(new AddCalc(), 2, 1), "n";
echo $calculator(new SubCalc(), 2, 1), "n";

18. interface Calc {
public function __invoke($left, $right);
}
class AddCalc implements Calc {
public function __invoke($left, $right) {
return $left + $right;
}
}
class SubCalc implements Calc {
public function __invoke($left, $right) {
return $left - $right;
}
}

19. if ($logType == 'echo') {
echo $message;
} else if ($logType == 'file') {
$logger->writeToFile($message);
}

20. Composition Over Inheritance
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21. Behavior vs. Dependencies
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22. Application

23. Plugins
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24. Service Locator
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25. Dependency Injection
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26. Event Driven Programming
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27. Aspect Oriented Programming
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28. Rules Engine
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29. Build Process
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30. Enterprise

31. Public API
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32. Service Oriented Architecture (SOA)
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33. Global Broadcast
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34. When to break OCP!?

35. When to break OCP!?
Separation of
concerns
Excessive Single
duplication responsibility
35

36. Everyday vs. the Revolutionary
Facts don't Feature
fit the doesn't fit
theory the design
36

37. What’s Your Strategy?

38. Questions?

39. Thanks You!