Complexity Metrics
And You
- dictionary.com
cost of complexity
Complex code is...
- Harder to read
- Harder to test
- 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
:(
code metaphors
"Technical Debt"
( but no technical interest )
"Code smell"
Bad News
Your code must change
Change increases complexity
"... unless work is done to maintain
or reduce [complexity]."
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/
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
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
- visualization across a project
- visualization over time
- github project
- examples
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
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
Use what helps; ignore the rest
Thanks.
Complexity Metrics And You
Complexity Metrics and You
By Jared Stilwell
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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