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Code metrics in PHP

This talk introduces some code metrics concepts with easy examples, and how to obtain them in PHP using tools like phploc, phpdepend, phpmetrics, etc. It follows with a discussion on which metrics are relevant, how we are already using them in some projects and how we should evaluate them in our department.

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Code metrics in PHP

  1. 1. Code metrics in PHP From lines to code semantic
  2. 2. ● Julio Martinez ● Developing PHP since 2001 ● 1.5 years working at Ulabox ● Find me: @liopic Code metrics in PHP: 0. Introduction Who am I?
  3. 3. ● El antisúper! ● 6-years-old startup ● 11 developers ● monolith & new services ● #rigor ● We are hiring! Code metrics in PHP: 0. Introduction What is Ulabox?
  4. 4. ● Evaluate quality! ● We need objective, reproducible and quantifiable metrics Could you tell me some examples of metrics? Code metrics in PHP: 1. Looking for quality Why do we need software metrics?
  5. 5. ● number of bugfixes per month ● lines of code ● test coverage ● number of user stories covered ● follows clean code’s rules ● documentation lines / total of code lines ● etc Code metrics in PHP: 1. Looking for quality Some examples?
  6. 6. ● Testing first! ● Code “surface” ● Lines grouping ● Code semantic Disclaimer: I’ll discuss locally-executable tools (non SaaS) ● SaaS: Insight, Code climate, Scrutinizer, SonarQube... Code metrics in PHP: 1. Looking for quality Let’s start our knowledge journey...
  7. 7. ● User stories: behat ● General testing: phpunit ○ Code coverage ○ Mutant testing (=test your tests): humbug ● Unit/spec testing: phpspec Code metrics in PHP. Testing Testing First!
  8. 8. ● Code sniffer (code style, PSR2): phpcs ● Copy+paste detector (DRY): phpcpd ● Clean code & common smells: ○ phpmd (“mess detector”, a bit old) ○ Exakat (it’s SaaS but has trial download) Code metrics in PHP: 3. Code surface Code “surface”
  9. 9. ● Counting lines: phploc ● Getting ratios: pdepend Code metrics in PHP: 4. Lines grouping Lines grouping
  10. 10. 1. Cyclomatic complexity (paths of execution) 2. Coupling metrics (relations between “modules”) 3. Lack of cohesion, LCOM (relations between methods) 4. Halstead’s metrics (operands and operators) 5. Maintainability Index Code metrics in PHP: 5. Code semantic Code semantic analysis
  11. 11. Code metrics in PHP: 5. Code semantic Cyclomatic complexity abstract class BaseBird { private $eggs = 0; public function makeEgg() { $this->eggs++; } public function crackEgg() { if ($this->eggs <=0) { throw new NoEggsException(); } $this->eggs--; } public function fly() { return 'flap-flap'; } abstract public function sound(); } class Duck extends BaseBird { public function sound() { return 'quack'; } public function swim() { return 'splash'; } } class Parrot extends BaseBird { public function sound() { $friend = new Duck(); if($friend->sound()){ return 'Err '.$friend->sound(); } return ''; } }
  12. 12. Code metrics in PHP: 5. Code semantic Cyclomatic complexity abstract class BaseBird { private $eggs = 0; public function makeEgg() { $this->eggs++; } public function crackEgg() { if ($this->eggs <=0) { throw new NoEggsException(); } $this->eggs--; } public function fly() { return 'flap-flap'; } abstract public function sound(); } class Duck extends BaseBird { public function sound() { return 'quack'; } public function swim() { return 'splash'; } } class Parrot extends BaseBird { public function sound() { $friend = new Duck(); if($friend->sound()){ return 'Err '.$friend->sound(); } return ''; } } 2 2 1
  13. 13. ● Afferent couplings (Ca) - “they use you” ● Efferent couplings (Ce) - “you use them” ● Instability, resilience to change (I): I = Ce / (Ce + Ca) ○ I=0 is a completely stable package ○ I=1 is a completely unstable package Code metrics in PHP: 5. Code semantic Coupling metrics
  14. 14. ● Abstractness (A): ratio of abstract classes ○ A=0 is a completely concrete package ○ A=1 is a completely abstract package ● Examples: ○ BaseBird: Ce=1 (uses NoEggsException), Ca=0; A=1, I=1 ○ Parrot, Ce=1 (uses Duck), Ca=0; A=0, I=1 ○ Duck, Ce=0, Ca=0; A=0, I=0 Code metrics in PHP: 5. Code semantic Coupling metrics
  15. 15. ● Distance from the main sequence (D): D = |A+I-1| ○ Balance between abstractness and stability ○ Ideal packages: (I=1, A=0), (I=0, A=1) Code metrics in PHP: 5. Code semantic Coupling metrics: main sequence
  16. 16. ● Groups of methods ● LCOM = 1 is ideal Code metrics in PHP: 5. Code semantic Lack of cohesion of methods (LCOM) abstract class BaseBird { private $eggs = 0; public function makeEgg() { $this->eggs++; } public function crackEgg() { if ($this->eggs <=0) { throw new NoEggsException(); } $this->eggs--; } public function fly() { return 'flap-flap'; } abstract public function sound(); }
  17. 17. ● Groups of methods ● LCOM = 1 is ideal ● BaseBird LCOM = 3 Code metrics in PHP: 5. Code semantic Lack of cohesion of methods (LCOM) abstract class BaseBird { private $eggs = 0; public function makeEgg() { $this->eggs++; } public function crackEgg() { if ($this->eggs <=0) { throw new NoEggsException(); } $this->eggs--; } public function fly() { return 'flap-flap'; } abstract public function sound(); }
  18. 18. ● η1 = number of distinct operators ● η2 = number of distinct operands ● N1 = the total number of operators ● N2 = the total number of operands ● Program vocabulary: η = η1 + η2 ● Program length: N = N1 + N2 Code metrics in PHP: 5. Code semantic Halstead complexity measures (1977)
  19. 19. ● Volume: V = N × log2 η (linearly with length, log with vocabulary) ● Difficulty : D = η1 /2 × N2 /η2 (half distinct operators, scarcity of operands) ● Effort: E = D × V ● Time required to program: T = E/18 seconds ● Delivered bugs: Code metrics in PHP: 5. Code semantic Halstead complexity measures
  20. 20. ● University of Idaho, Oman and Hagemeister ● Volume (V), Cyclomatic Complexity (G), Lines of Code (LOC) ● Original MI = 171 - 5.2*ln(V) - 0.23*G - 16.2*ln(LOC) Code metrics in PHP: 5. Code semantic Maintainability Index (1991)
  21. 21. ● phpmetrics ○ Let’s see all those indexes! Code metrics in PHP: 5. Code semantic Coupling + LCOM + Halstead + MI Maintainability.................... 65.83 / 100 Accessibility for new developers... 41.03 / 100 Simplicity of algorithms........... 42.57 / 100 Volume............................. 64.90 / 100 Reducing bug's probability......... 65.57 / 100
  22. 22. ● MUST! ○ phpcs - code sniffer - No extra effort need; always ○ phpunit - integration & unit tests - Write tests; always ● Adopt ○ phpspec - unit/specs - Write tests; always ○ behat - user stories (functional tests) - Write user stories; always ○ phpcpd - copy & paste - No effort; always ○ phpmetrics - No effort; main indexes weekly, others when refactor ● Give a try ○ humbug - test your tests - No effort; often ○ SaaS options - Customization effort; always Code metrics in PHP: 6. Summing up! RADAR of tools (how? when?)
  23. 23. Code metrics in PHP: 6. Summing up! Questions?
  24. 24. Code metrics in PHP: 6. Summing up! Thank you!

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