Complexity Metrics

And You






"so complicated or intricate as to be hard to understand or deal with"

- dictionary.com

cost of complexity


Complex code is...

  1. Harder to read
  2. Harder to test
  3. Harder to debug

Cheap to produce
Costly to maintain


http://www.trashsociety.com/2010/11/26/the-junk-drawer-trashogram/






Your code has at least one junk drawer

( probably several )






Things aspire to junkiness
Second Law of Thermodynamics (loosely translated)

Lehman's Laws


"[a system] must be continually adapted or it becomes progressively less satisfactory."

"As [a system] evolves its complexity increases unless work is done to maintain or reduce it."
http://en.wikipedia.org/wiki/Lehman's_laws_of_software_evolution





Usage  -->  Modification  -->  Complexity

:(

code metaphors



"Technical Debt"
( but no technical interest )


"Code smell"


"Broken Windows"

Bad News




Your code must change

Change increases complexity




"... unless work is done to maintain
or reduce [complexity]."


Multiple Layers

of Defense


  • Linting
  • Version control
  • Automated testing
  • Code Reviews
http://ariya.ofilabs.com/2012/12/quality-code-via-multiple-layers-of-defense.html

Feedback


Linting = cheap but limited
--------------------------------- the gap -----------------------------------
Testing = cheap-ish but incomplete

Version Control  = indirect and incomplete 

Code Reviews = super expensive and inconsistent

Metrics

We can use to numbers to track things!

source: http://measuringupblog.com/2013/11/13/are-you-covering-all-of-your-measurement-bases/




This is not dogma, it's engineering.


Halstead Metrics


"The Hydra"

Maurice H. Halstead

1973
Operators
&
Operands
-->


Given:

r = # of distinct operators
n = # of distinct operands
R = # of total operators
N = # of total operands
then...
everyone is now asleep
http://en.wikipedia.org/wiki/Halstead_complexity_measures

The Chase


  • Defines measurable properties as formulas
  • They build on each other to describe relationships
  • Not all of these measure complexity
  • Some worth mentioning:
    • Volume
    • Difficulty
    • Effort = Difficulty * Volume
    • Estimated Bugs = Volume / 3000


Cyclomatic Complexity


"Old Reliable"
(never image search for "old reliable" when preparing for a talk)

Thomas J. McCabe

1976
 -->





  • Based only on control flow
  • Measures unique paths
  • Gives an ideal number of tests


Maintainability Index


"One [metric] to Rule Them All"

Paul Oman &
Jack R. Hagemeister

1991

171 - 
5.2 * ln( Halstead Volume ) -
0.23 * ( Cyclomatic complexity ) -
16.2 * ln( Line count )





  • Aggregate of several other metrics
  • Scale from -Infinity to 171 (higher is better)
  • Two variants
    • original
    • comment-sensitive



JSHint


  • maxcomplexity
  • maxdepth
  • maxparams
  • maxstatements


complexity report




Plato



JSComplexity.org


Phil Booth & Perry Harlock

It covers other common metrics not seen here.

"Basically a strictly better  version
of this talk in website form. "
- me, just now


The wrap up


Your code loses value over time

Mind the complexity of changing code

Metrics can help

This is not a solved problem.
Use what helps;  ignore the rest




Thanks.




Complexity Metrics and You

By Jared Stilwell

Made with Slides.com

Complexity Metrics and You

A brief introduction to the concept of complexity in software, the effects it has over time, and several tools to help you spot and contain it.

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