No Reuse Before Use

terry@odd-e.com

Who Am I

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• I am Terry Yin!• Work for Odd-e!• Experienced in software development!• Focus on technical coaching!• Love programming!• A father

Me

This talk is about

ReuseUse

Working Software That Has Customer Value

Software

Design Patterns

Common Platform Library

Framework

Object Oriented DesignGeneric Programming

Meta Pr

ogram

mingMiddleware

Domain ModellingOpen Source

3rd Party

Java

Let’s Visit A City !On The Opposite Side of the Globe

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Planned City

Oscar Niemeyer

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10,000 pedestrian lives are lost on Brazilian road in

2012, whom in theory do not existing in Brasilia.!

(270, 000 around the world)

"Organic planning does not begin with a preconceived goal; it moves from need to need, from opportunity to opportunity, in a series of adaptations that themselves become increasingly coherent and purposeful, so that they generate a complex final design, hardly less unified than a pre-formed geometric pattern.” !— Lewis Mumford explained further what he admired in medieval cities

what if design from use …

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Software Reuse

what our graphic designer thinks it is

what programmers think it is what architects think it is

what customers think it is what managers think it is what really happens

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what our graphic designer thinks about reuse

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Why cannot the graphic designer think about something more

abstract?

Software developers are!trained in!

abstract thinking

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what programmers think about reuse

Duplication

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Duplication may be the root of all evil in

software.

Clean Code, Robert C. Martin

If Copy-Paste Is Bad• What about designing a library?!• What about inheritance?!• What about composition?!• What about using a framework?

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Maybe Yes, Maybe No. Stop Speculating, and make something that works first!

Refactoring• Small steps!• Look for code smells!• Following design principles!

- SOLID!- High cohesion, low coupling!- Once And Only Once!

• Design emerges from working code

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"Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure."

Refactoring: Improving the Design of Existing Code by Martin Fowler

Pattern Or Anti-Pattern

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If you’d like to become a better software designer, studying the evolution of great software designs will be more valuable than studying the great designs themselves. For it is in the evolution that the real wisdom lies.

Refactoring to Patterns, Joshua Kerievsky

Emergent Design

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Code, listen you shall.

Let the design be the way it wants to be!

Why Upfront Design Fails?

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what architects think about reuse

The Second-System Effect

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when an architect designs a second system, it is the most dangerous system he will ever design, because he will tend to incorporate all of the additions he

originated but did not add to the first system due to inherent time constraints. Thus, when embarking

upon a second system, an engineer should be mindful that he is susceptible to over-engineering it.

Mythical Man Month (1974), Fred Brooks

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In theory, traditional design tries to make all design decision during speculation

In practice, we can’t

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1.Make it work

2.Make it right

3.Make it fast

— Kent Beck, inventor of XP

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what customers think about reuse

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Design from the perspective of use!rather than implementation

Customer Value

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People do not on the whole pay for (or need) generality: They tend to have a specific situation, and it is a solution to that specific situation that has value.

Simplicity before generality, use before reuse,!by Kevlin Henney

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what managers think about reuse

Reusability Is Not Free

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… I see that expense (of making reusable code) as exactly the effort of productising the component, discussed

in Chapter 1. So my estimate of the effort ratio would be threefold.

Mythical Man Month (1974), Fred Brooks

Reuse Is Not Free, Either

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What’s worse than ‘copy-paste programming’ is ‘google then copy-

paste without understanding it.

All non-trivial abstractions, to some degree, are leaky.The Law of Leaky Abstractions by Joel Spolsky

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what really happens when reuse before use

Project Or Product• When you make a product like a project!• you get Brasilia

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What Should We Do?Only build software for

specific needs.!Build reusable parts, and

apply them in specific applications.!Start from building for

specific needs, then generalise from them gradually.

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there is no such thing as reusable software, only software that has been reused.

Goals over means!Once-And-Only-Once over reusability!

Simplicity before generality!Use before reuse

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That is, while there is value in the items on the right, we value the items on the left more.

You’ve reached the end

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Thanks!