Pair Programming Langr Software Solutions Originally presented to the Phoenix XP Users Group, October 2002 Last updated 2010

Pair Programming

Langr Software SolutionsOriginally presented to the Phoenix XP Users Group, October 2002

Last updated 2010

Copyright © 2010 by Langr Software Solutions. All Rights Reserved.

Pairing

Two programmersJointly developing production softwareNot “I watch over your shoulder”(That sounds like it would be waste of time!)


DynamicsMust pair if askedTwo roles in the pair: Strategic Tactical

Developers switch roles frequentlyRhythm


Mechanics

Comfortable workstations Accommodate two side by side Separate or shared input devices

Switch pairs at least once a day 3x / day?

Core pairing hoursTake breaks!


Technique Variants

Ping-pong pairing I code test, you code solution; we

switch

Promiscuous pairing Least-skilled remains on task

Promiscuous keyboarding Keyboarder switches every minute

Face-to-face


Additional Guidelines

5-minute argument rule5-second typo ruleBe attentive!


Review

Goals: Remove defects Prevent similar mistakes in future Generate useful dataPairing != formal review process Different costs, focus, outcomes


Formal Review Challenges

Disinterested parties That weren't involved in creating

solution View product of others as a distraction Find mostly low-hanging fruit

Anything occurring after the fact... Often doesn't get done or done well Often doesn't result in changes

Pairing invests the “reviewer”


Context Switching

Incurs overhead costShould drive toward cleaner solutionFocus on “unit test cases as doc”Task owner describes current test case New partner helps flesh out test Can quickly understand how to realize

shouldDoSomethingWhenThisCondition


General Benefits

Continual reviewCoverageMinimized personnel dependenciesImproved designMinimized defectsSustainableMore rapid solutions


Additional Benefits

Improved understandingMinimizes open workspace distractionsConsistent pacing Individuals less likely to bog down

Team members rise to common levelIncreased collaboration Helps build a true team


Management Benefits

Reduced risk (better truck number!)Rapid training for new hiresInterviewing criteriaProblems less hiddenPeer pressureResource fluidityCross-pollination


Developer Benefits

Awareness of other parts of systemResume buildingDecreased time in (review) meetingsContinuous educationAbility to move between teamsRapid learning as new hireThe little things

e.g. Eclipse shortcuts


“But it takes twice as long…”

Consider: Debugging sessions Increased cost of change due to poorer

design Mull time Inconsistent team abilities Learning time


Studies

“Costs and Benefits of Pair Programming” Laurie Williams, Alistair Cockburn Pair: 15% slower Error free code went from 70% to 85%

"The Effect of Pairs in Program Design Tasks" Lui, KM, et al, IEEE Transactions, 2008

"Evaluating Pair Programming with Respect to System Complexity and Programmer Expertise" Arisholm, E. +84% effort to perform tasks correctly More complex systems: +48% correct solutions


IssuesPair dynamics Extrovert and Introvert mixes Expert and Novice mixesNot everyone can work this way If done well, many like it Some dislike but appreciate its benefits A small percentage will refuseSocial preferences / cultureFearPersonal habits


“I Like My Space”

You can still have itBut... building software is a team activityFind a balance between pairing and not Never mandate all or nothing


Other Considerations

Odd # of team membersCore hoursTeam of 1 - 2Distributed developersContext switching overhead


When Not Pairing

Meetings, email, documents, etc.Review existing code Analyze to understand of design/defect Determine areas for potential

refactoring

Spike solutionsBuild tools or AT frameworkIf you must work on production code: Come up with ground rules Do post-development inspections


Where Do I Start?Discuss it with your teamAgree on the values you want to deriveCreate an initial simple set of rules Revisit regularly

Learn to pair first To learn when not to pair

Influence through metrics If necessary, track pairing vs. not

Re-assess value regularlyEnsure a coach monitors interaction issues


Further Reading

http://en.wikipedia.org/wiki/Pair_programming

Atwood, Jeff. http://www.codinghorror.com/blog/archives/

000999.html

Langr, Jeff. http://langrsoft.com/articles/pairing.shtml

Agile Alliance articles in category Pair Programming

Documents

Pair Programming Langr Software Solutions Originally presented to the Phoenix XP Users Group, October 2002 Last updated 2010