1. Replacing
Conditionals With
Polymorphism
@gpespn

2. “Any fool can write code that a
computer can understand.
Good programmers write code
that humans can understand.”
-- Martin Fowler
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3. @gpespn
But why?
• Easier to read
• Maintainability
• Extensibility
• Isolation of change
• Easier to test

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B+

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C-

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New Feature!
Guest sessions

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F-

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I just want to
send a message
to an object

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-W
oof!
-M
eow
!

11. @gpespn
Polymorphism
tell don't ask

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15. @gpespn
still have conditional!

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Create a high
level abstract
class

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Abstract Subclass Subclass

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Polymorphism

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Whats the catch?
• Parallel interfaces
• Design patterns that are confusing to those unfamiliar
to them
• New words/vocabulary into application. LOC went up!
• Increased big picture complexity in exchange for
macro clarity
• Too many Objects

22. @gpespn

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Questions?