Managing Duplicated Code with Linked Editing

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Managing Duplicated Codewith Linked Editing

• Michael Toomim, Andrew Begel and Susan L. Graham
• Harmonia Research Group
• University of California at Berkeley

Visual Languages and Human-Centric Computing
September 9, 2004
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Duplicated Code
is
Bad
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The simplest system must contain
no duplicate code
Kent Beck
Extreme Programming Explained
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1 in the stink parade is
duplicated code.
Martin Fowler
Refactoring
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DRY Dont Repeat Yourself
Andrew Hunt and David Thomas
The Pragmatic Programmer
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Duplicated Code is Bad

• Causes verbosity/bloat, viscous edits,
  inconsistency, difficult maintainability

• But it will always exist
• Linked Editing makes it easy to work with

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How do they manage it?
Abstraction.
The solution to duplication.
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50 Years of Abstraction

• Functions, macros, objects, templates, aspects,
  generative programs, traits
• Language abstractions since Fortran

• Tools to help programmers find and refactor
  duplication
• 16 duplication finding algorithms published in
  last 14 years
• Refactoring supported in mainstream IDEs

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Duplication is Everywhere
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Why We Duplicate Code

• Abstractions have usability problems
• Difficult to create
• Can make code worse
• Can be impossible to express
• Programmers have no other alternative

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Solution Linked Editing

• Editor provides enhanced interaction
• Visualization, navigation, simultaneous editing
  of duplication

• Addresses the problems of duplication without the
  costs of abstraction
• Implemented in editor called Codelink

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User Study

• 13 subjects (novice to expert)
• Programming tasks with both Codelink and
  functional abstraction
• Measurements
• Time to abstract or link duplicated code
• Benefits of the abstraction or link during
  programming tasks (rated by subjects)

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Results Creating a Link

• Mean abstraction time 1306 minutes
• Mean link time 0022 seconds

!
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Working with Linked Code
Rated benefits of abstraction and Codelink over
duplicated code
Much Better
Moderately Better
Slightly Better
Same
Slightly Worse
Speed
Effort
Changeability
Maintainability
Understandability
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Linked Editing Worked

• Provided benefits comparable to abstraction
• but required very little programming time

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Future Research Directions

• Improved difference analysis
• Integrate with refactoring systems
• Find duplicated code automatically
• Refactor linked code automatically
• Linked Editing of other digital documents
• Spreadsheets, web sites, music scores, these
  PowerPoint slides

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Contributions

• Linked Editing
• Manages duplicated code effectively
• Easy to learn and use
• Applicable in many domains

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Michael Toomimtoomim_at_cs.berkeley.edu