User:Jeroen De Dauw/Static: The S in STUPID

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• The S in STUPID

  YES

  Caturday will not be stopped!

  

• The S in STUPID

  YES

  public function doStuff() {
      // ...
  
      Logger::log( 'doing stuff during caturday is madness' );
  
      // ...
  
      DataStore::saveObject( $object );
  
      // ...
  }
  

  • What are the problems with this code?

• The S in STUPID

  YES

  Tight coupling!

  Problem #1:

  • This class is now dependent on Logger and DataStore.

  public function doStuff() {
      // ...
  
      Logger::log( 'doing stuff during caturday is madness' );
  
      // ...
  
      DataStore::saveObject( $object );
  
      // ...
  }
  

• The S in STUPID

  YES

  Tight coupling!

  Problem #2:

  • What if the caller wants to use a different logger?

  public function doStuff() {
      // ...
  
      Logger::log( 'doing stuff during caturday is madness' );
  
      // ...
  
      DataStore::saveObject( $object );
  
      // ...
  }
  

  • Logger::log and DataStore::saveObject are ALWAYS called

• The S in STUPID

  YES

  Tight coupling!

  public function testDoStuff() {
  
      // Cannot prevent disk and database writes
      // State might be leaked, order might become relevant
      $object->doStuff();
  
  }
  

  public function doStuff() {
      // ...
  
      Logger::log( 'doing stuff during caturday is madness' );
  
      // ...
  
      DataStore::saveObject( $object );
  
      // ...
  }
  

  • Not just tests, applies to all code making use of doStuff.

• The S in STUPID

  YES

  Tight coupling!

  public function doStuff() {
      // ...
  
      Logger::log( 'doing stuff during caturday is madness' );
  
      // ...
  
      DataStore::saveObject( $object );
  
      // ...
  }
  

  class DataStore {
  
      public function saveObject( $object ) {
          $loadBalancer = LoadBalancerFactory::getInstance();
  
          // ...
  
          $database->update( /* ... */ );
  
          // ...
  
          Logger::log( 'done saving object' );
      }
  
  }
  

  • You cannot use a part of the system without initializing whole chuncks of it
  • Hard to fix once pervailent through the codebase

• The S in STUPID

  YES

  Fixing the problem

  class Logger {
  
      public static function log() {
          // ...
      }
  
      public static function resetForTesting() {
          // ...
      }
  
  }
  

• The S in STUPID

  YES

  Fixing the problem

  public function doStuff() {
      // ...
  
      Logger::getInstance()->log( 'doing stuff during caturday is madness' );
  
      // ...
  }
  

• The S in STUPID

  YES

  Fixing the problem

  public function doStuff( Logger $logger, DataStore $dataStore ) {
      // ...
  
      $logger->log( 'doing stuff during caturday is madness' );
  
      // ...
  
      $dataStore->saveObject( $object );
  
      // ...
  }
  

  • Where Logger and DataStore are properly seggeragted interfaces

  public function testDoStuff() {
      // ...
  
      // Create simple mocks
      $logger = new NullLogger();
      $dataStore = new MockDataStore();
  
      $object->doStuff( $logger, $dataStore );
  
      // ...
  }
  

• The S in STUPID

  YES

  What about this static call?

  class Awesome {
  
      public function calculateAwesomeness() {
          // ...
  
          // Clearly this can never be negative
          return Math.Abs( $awesomeness );
      }
  
  }
  

• The S in STUPID

  YES
  • Static calls to leaves in the call graph are less evil
  • Leaves can stop being leaves

  class Awesome {
  
      public function calculateAwesomeness() {
          Utils::getAwesomeFactor();
  
          // ...
      }
  
  }
  

  class Utils {
  
      public static function getAwesomeFactor() {
          return 42;
      }
  
  }
  

  • What if the awesome factor is now stored in a config file or db?

• The S in STUPID

  YES
  • Static code is procedural, not OOP
  • Static is almost always bad, causing tight coupling, thus avoid it
  • Both static and non-static code in a class suggests violation of single responsibility
  

• The S in STUPID

  YES

  Further reading

  • SOLID (article)
  • STUPID (blog post)
  • 10 things that make your code hard to test (blog post)
  • Testable code (screencast)