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Clean Code - quick summary
● Naming
● Small functions
● Meaningful comments
● Data abstraction
● Error Handling
● TDD(Unit Tests)
● Building Systems
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Goals
At working at module level, software structure should
● Tolerate changes
● Easy to understand
● Basic components for reuse
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Our Enemies
● Rigidity - difficult to change
● Fragility - easy to break
● Immobility - difficult to reuse
● Viscosity - resistance against making changes
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SOLID Principles
● Single Responsibility
● Open-closed
● Liskov substitution
● Interface segregation
● Dependency Inversion
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Single Responsibility Principle (SRP)
● A module should be responsible to
one, and only one, actor
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SRP: Violation
Employee
-regularHours
+calculatePay
+reportHours
+save
Roy
John
Zune
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SRP: Solution
Employee
Facade
+calculatePay
+reportHours
+save
PayCalculator
+calculatePay
HourReporter
+reportHours
EmployeeSaver
+save
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Open-closed Principle
● Open for extension but closed for
modification
● Example with inheritance
○ Bad
○ Good
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Liskov Substitution Principle
● If for each object o1 of type S, there is an object o2 of type T, such that, for all
programs P defined in terms of T, the behavior of P is unchanged when o1 is
substituted for o2, then S is a subtype of T
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LSP Violation
Rectangle
+setHeight
+setWidth
Square
+setSides
User
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Interface Segregation Principle (ISP)
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ISP Violation
Ops
+ops0
+ops1
+ops2
User0 User1 User2
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Dependency Inversion Principle
● Source code should interact with
abstractions, not concretions
● Stable vs volatile concrete elements
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Takeaways
● Consider actors in the system
● Keep options open with layers
● Interact with abstractions over details