Skip to content

FrOSCon - Fixing Legacy Code

By Benjamin Eberlei and Kore Nordmann.

What Is Legacy Code

  • hard or impossible to fix errors or implement new features
  • hard or impossible to implement automatic testing

What Is The Talk About

Issues With Legacy Code

  • code issues
  • inversion of control
  • data structures
  • application or business logic
  • shared state

Code Issues

  • code size
  • high efferent coupling
  • code duplication
  • ...
  • Use phpmd to locate size or complexity errors.

Efferent Coupling

  • many outgoing coupling for one class in other classes
  • can be located with pdepend

Inversion Of Control

  • Missing abstractions
  • Inline new
  • Static calls
  • Inline life cycle management (only value objects and exceptions should be newed inline)

Data Structure

  • Missing abstractions
  • Inline new
  • Static calls
  • Inline life cycle management (only value objects and exceptions should be newed inline)

Data Structure

  • with arrays, you have a bad documentation
  • use simple value objects (also known as dto) and they are not immutable
  • split logic and try to avoid big models (seperation of concerns (roles/contextes) on model logic
  • branch by abstraction
    • introduce facade / proxy for old code
    • call old code from facade / proxy implementation
    • write new shiny facade / proxy implementation
    • use new implementation
    • delete old code

Application Or Business Logic

  • mixed business logic (application logic) in large controllers is the most common and pressing issue with legacy code (fat controllers)
  • try to use solutions like business requirement
  • extract business logic like service layer pattern
  • introduce (domain) events (in the same request)
  • introduce message queues (not in the same request)

Shared State

  • we know that global state is bad
  • sessions are (often) cross-request global state in bash maps
  • method execution pathes depending on current object state are horrible to track down

Testing Changes

  • if your legacy code is hard to test, try to test it from the http protocoll point of view
  • use behat as behaviour driven development (BDD)
  • use mink with "goute", "sahi" or "zombie.js", "selenium", "selenium 2"

Extra

  • do small checks when refactoring (good indicator are many, many commits)
  • test your primary use cases (put the chaos in the cage)
  • be bold (enough) and remove old code

Translate to de es fr it pt ja

Trackbacks

No Trackbacks

Comments

Display comments as Linear | Threaded

No comments

Add Comment

Standard emoticons like :-) and ;-) are converted to images.
E-Mail addresses will not be displayed and will only be used for E-Mail notifications.
To leave a comment you must approve it via e-mail, which will be sent to your address after submission.

To prevent automated Bots from commentspamming, please enter the string you see in the image below in the appropriate input box. Your comment will only be submitted if the strings match. Please ensure that your browser supports and accepts cookies, or your comment cannot be verified correctly.
CAPTCHA

Markdown format allowed
Form options