Viking Code School Presents Christopher Hendrix of Pivotal Labs

@materialdesignr #goodobjects What Makes a Good Object? Christopher Hendrix

@materialdesignr #goodobjects This talk’s Presenter

@materialdesignr #goodobjects This talk’s • How to make objects/methods that
are: • Sane • Confident • Consistent Goal

@materialdesignr #goodobjects This talk’s Guide

@materialdesignr #goodobjects This talk’s • 5 Family Member “Guiding Principles”
• Quote • Theory/Introduction • Code Examples • Summary • Extra Reading • Q&A Structure

@materialdesignr #goodobjects Think like a Teenager

@materialdesignr #goodobjects ―Teenager “I will never grow up.”

@materialdesignr #goodobjects Think like a • Values vs Entities •
Colors/Numbers vs People  • Can a Person be a Value Type? • Is teleportation murder? Teenager

@materialdesignr #goodobjects Think like a Teenager • Fundamental Attributes

@materialdesignr #goodobjects Think like a Teenager • Fundamental Attributes Start
End Duration

@materialdesignr #goodobjects Think like a Teenager • Fundamental Attributes •
Computed Properties Start End Duration

@materialdesignr #goodobjects Think like a Teenager • Designated Initializer  •
Custom Initializers

@materialdesignr #goodobjects Think like a Teenager • What about  
Freeform Objects?

@materialdesignr #goodobjects Think like a Teenager • “Subtyping”

@materialdesignr #goodobjects Think like a Teenager • Hide your “Subtyping”

@materialdesignr #goodobjects Think like a • Separate Fundamental Attributes from
Computed Properties • Think of a single Designated Initializer • Use Custom Initializers which delegate • Hide your “Subtyping” Teenager

@materialdesignr #goodobjects Think like a Child

@materialdesignr #goodobjects ―Child “But you promised!”

@materialdesignr #goodobjects • f(x) = x^2 • A transformation •
What makes f(x) a Good Function? Think like a Child

@materialdesignr #goodobjects “A function is a relation between a set
of inputs and a set of permissible outputs with the property that each input is related to exactly one output.” All Integer 1 2 3 ⋮ + Integer 1 4 9 ⋮

@materialdesignr #goodobjects • f(x) = x^2 • A Good Function
has • Consistent Input Types • Consistent Output Types • Well defined relation from each input to output Think like a Child Integer 1 2 3 ⋮ Integer 1 4 9 ⋮

@materialdesignr #goodobjects Think like a Child

@materialdesignr #goodobjects Think like a • Think of your function’s
Type Signatures • Have consistent outputs • Use Arrays to encode potential failure Child

@materialdesignr #goodobjects Think like an Adult

@materialdesignr #goodobjects ―Adult “No.”

@materialdesignr #goodobjects Think like an • Not everyone else makes
good functions • Function dependencies are   sources of uncertainty Adult

@materialdesignr #goodobjects Think like an Adult

@materialdesignr #goodobjects Think like an Adult • Reject Unworkable Values 

@materialdesignr #goodobjects Think like an Adult • NaN 

@materialdesignr #goodobjects Think like an Adult • Does this help? 

@materialdesignr #goodobjects Think like an Adult • Reject Values at
entry points

@materialdesignr #goodobjects Think like an Adult • Wrap External Objects

@materialdesignr #goodobjects Think like an • Say No to bad
dependencies • Earliest Possible Rejection • Wrap External Objects in Confident Values Adult

@materialdesignr #goodobjects Think like a Senior

@materialdesignr #goodobjects ―Senior “Who are you?”

@materialdesignr #goodobjects Think like a Senior

@materialdesignr #goodobjects Think like a Senior • Accessing Data

@materialdesignr #goodobjects Think like a • Is it really Data?
• Functions vs. Methods vs. Messages Senior @materialdesignr Sally Bob Age:  24 24

• Functions vs. Methods vs. Messages Senior Sally Bob Age:  24 29 Age? def age if trying_to_impress? return @age + 5 else return @age end end

• Functions vs. Methods vs. Messages • Same Message, Different Methods Senior Sally Harry Age:  32 32 Age? def age # I’m honest return @age end

@materialdesignr #goodobjects Think like a Senior • Queries • Commands

@materialdesignr #goodobjects Think like a • There is No Data,
Only Zuul Messages • Ask Nicely instead of grabbing internals • Tell Confidently instead of DIY Senior

@materialdesignr #goodobjects Think like a Baby

@materialdesignr #goodobjects ―Baby “Who am I?”

@materialdesignr #goodobjects Think like a • What’s so special about
me? • Everything is message sending • Messages to Self Baby

@materialdesignr #goodobjects Think like a Baby

@materialdesignr #goodobjects Think like a Baby • Accessing Data

@materialdesignr #goodobjects Think like a Baby • Messages to Self
• Information Hiding

@materialdesignr #goodobjects Think like a • Other Methods should be
treated like Other Objects • Hide your own data Baby

@materialdesignr #goodobjects This talk’s • Teenager — Make your constructors
matter • Child — Think about function signatures • Adult — Use errors to prevent unknown state • Senior — Send messages to other objects • Baby — Send messages to yourself Summary

@materialdesignr #goodobjects Reading is Practical Object Oriented Design in Ruby 
―Sandi Metz Confident Ruby  ―Avdi Grimm Refactoring  ―Martin Fowler Fundamental

@materialdesignr #goodobjects Questions & Answers

@materialdesignr #goodobjects This talk’s • www.materialdesignr.com • @materialdesignr • github.com/chendrix
• linkedin.com/in/materialdesignr Self-Promotion

Viking Code School Presents Christopher Hendrix...

Viking Code School Presents Christopher Hendrix of Pivotal Labs

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