============
Design Rules
============

The Design Ruleset contains a collection of rules that find software design related problems.

ExitExpression
==============

Since: PHPMD 0.2

An exit-expression within regular code is untestable and therefore it should be avoided. Consider to move the exit-expression into some kind of startup script where an error/exception code is returned to the calling environment.

Example: ::

  class Foo {
      public function bar($param)  {
          if ($param === 42) {
              exit(23);
          }
      }
  }

EvalExpression
==============

Since: PHPMD 0.2

An eval-expression is untestable, a security risk and bad practice. Therefore it should be avoided. Consider to replace the eval-expression with regular code.

Example: ::

  class Foo {
      public function bar($param)  {
          if ($param === 42) {
              eval('$param = 23;');
          }
      }
  }

GotoStatement
=============

Since: PHPMD 1.1.0

Goto makes code harder to read and it is nearly impossible to understand the control flow of an application that uses this language construct. Therefore it should be avoided. Consider to replace Goto with regular control structures and separate methods/function, which are easier to read.

Example: ::

  class Foo {
      public function bar($param)  {
          A:
          if ($param === 42) {
              goto X;
          }
          Y:
          if (time() % 42 === 23) {
              goto Z;
          }
          X:
          if (time() % 23 === 42) {
              goto Y;
          }
          Z:
          return 42;
      }
  }

NumberOfChildren
================

Since: PHPMD 0.2

A class with an excessive number of children is an indicator for an unbalanced class hierarchy. You should consider to refactor this class hierarchy.

This rule has the following properties:

+-----------------------------------+---------------+---------------------------------------------+
| Name                              | Default Value | Description                                 |
+===================================+===============+=============================================+
| minimum                           | 15            | Maximum number of acceptable child classes. |
+-----------------------------------+---------------+---------------------------------------------+

DepthOfInheritance
==================

Since: PHPMD 0.2

A class with many parents is an indicator for an unbalanced and wrong class hierarchy. You should consider to refactor this class hierarchy.

This rule has the following properties:

+-----------------------------------+---------------+----------------------------------------------+
| Name                              | Default Value | Description                                  |
+===================================+===============+==============================================+
| minimum                           | 6             | Maximum number of acceptable parent classes. |
+-----------------------------------+---------------+----------------------------------------------+

CouplingBetweenObjects
======================

Since: PHPMD 1.1.0

A class with too many dependencies has negative impacts on several quality aspects of a class. This includes quality criteria like stability, maintainability and understandability

Example: ::

  class Foo {
      /**
       * @var \foo\bar\X
       */
      private $x = null;
  
      /**
       * @var \foo\bar\Y
       */
      private $y = null;
  
      /**
       * @var \foo\bar\Z
       */
      private $z = null;
  
      public function setFoo(\Foo $foo) {}
      public function setBar(\Bar $bar) {}
      public function setBaz(\Baz $baz) {}
  
      /**
       * @return \SplObjectStorage
       * @throws \OutOfRangeException
       * @throws \InvalidArgumentException
       * @throws \ErrorException
       */
      public function process(\Iterator $it) {}
  
      // ...
  }

This rule has the following properties:

+-----------------------------------+---------------+----------------------------------------------+
| Name                              | Default Value | Description                                  |
+===================================+===============+==============================================+
| maximum                           | 13            | Maximum number of acceptable dependencies.   |
+-----------------------------------+---------------+----------------------------------------------+

DevelopmentCodeFragment
=======================

Since: PHPMD 2.3.0

Functions like var_dump(), print_r() etc. are normally only used during development and therefore such calls in production code are a good indicator that they were just forgotten.

Example: ::

  class SuspectCode {
  
      public function doSomething(array $items)
      {
          foreach ($items as $i => $item) {
              // …
  
              if ('qafoo' == $item) var_dump($i);
  
              // …
          }
      }
  }

This rule has the following properties:

+----------------------------------+--------------------------------------------------------+---------------------------------------------------------+
| Name                             | Default Value                                          | Description                                             |
+==================================+========================================================+=========================================================+
| unwanted-functions               | var_dump,print_r,debug_zval_dump,debug_print_backtrace | Comma separated list of suspect function images.        |
+----------------------------------+--------------------------------------------------------+---------------------------------------------------------+
| ignore-namespaces                | false                                                  | Ignore namespaces when looking for dev. fragments       |
+----------------------------------+--------------------------------------------------------+---------------------------------------------------------+

EmptyCatchBlock
===============

Since: PHPMD 2.7.0

Usually empty try-catch is a bad idea because you are silently swallowing an error condition and then continuing execution. Occasionally this may be the right thing to do, but often it's a sign that a developer saw an exception, didn't know what to do about it, and so used an empty catch to silence the problem.

Example: ::

  class Foo {

      public function bar()
      {
          try {
              // ...
          } catch (Exception $e) {} // empty catch block
      }
  }

CountInLoopExpression
=====================

Since: PHPMD 2.7.0

Using count/sizeof in loops expressions is considered bad practice and is a potential source of
many bugs, especially when the loop manipulates an array, as count happens on each iteration.

Example: ::

  class Foo {

    public function bar()
    {
      $arr = array();

      for ($i = 0; count($arr); $i++) {
        // ...
      }
    }
  }

Remark
======

  This document is based on a ruleset xml-file, that was taken from the original source of the `PMD`__ project. This means that most parts of the content on this page are the intellectual work of the PMD community and its contributors and not of the PHPMD project.

__ http://pmd.sourceforge.net/