Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Since: PHPMD 0.1

The NPath complexity of a method is the number of acyclic execution paths through that method. A threshold of 200 is generally considered the point where measures should be taken to reduce complexity.

Example:

class Foo {
      function bar() {
          // lots of complicated code
      }
  }

Source: http://phpmd.org/rules/codesize.txt

Since: PHPMD 0.1

Complexity is determined by the number of decision points in a method plus one for the method entry. The decision points are 'if', 'while', 'for', and 'case labels'. Generally, 1-4 is low complexity, 5-7 indicates moderate complexity, 8-10 is high complexity, and 11+ is very high complexity.

Example:

// Cyclomatic Complexity = 11
  class Foo {
  1   public function example() {
  2       if ($a == $b) {
  3           if ($a1 == $b1) {
                  fiddle();
  4           } elseif ($a2 == $b2) {
                  fiddle();
              } else {
                  fiddle();
              }
  5       } elseif ($c == $d) {
  6           while ($c == $d) {
                  fiddle();
              }
  7        } elseif ($e == $f) {
  8           for ($n = 0; $n < $h; $n++) {
                  fiddle();
              }
          } else {
              switch ($z) {
  9               case 1:
                      fiddle();
                      break;
  10              case 2:
                      fiddle();
                      break;
  11              case 3:
                      fiddle();
                      break;
                  default:
                      fiddle();
                      break;
              }
          }
      }
  }

Source: http://phpmd.org/rules/codesize.txt

Since: PHPMD 1.4.0

An if expression with an else branch is never necessary. You can rewrite the conditions in a way that the else is not necessary and the code becomes simpler to read. To achieve this use early return statements. To achieve this you may need to split the code it several smaller methods. For very simple assignments you could also use the ternary operations.

Example:

class Foo
  {
      public function bar($flag)
      {
          if ($flag) {
              // one branch
          } else {
              // another branch
          }
      }
  }

Source: http://phpmd.org/rules/cleancode.txt

Since: PHPMD 1.4.0

An if expression with an else branch is never necessary. You can rewrite the conditions in a way that the else is not necessary and the code becomes simpler to read. To achieve this use early return statements. To achieve this you may need to split the code it several smaller methods. For very simple assignments you could also use the ternary operations.

Example:

class Foo
  {
      public function bar($flag)
      {
          if ($flag) {
              // one branch
          } else {
              // another branch
          }
      }
  }

Source: http://phpmd.org/rules/cleancode.txt

Since: PHPMD 0.2

Detects when a local variable is declared and/or assigned, but not used.

Example:

class Foo {
      public function doSomething()
      {
          $i = 5; // Unused
      }
  }

Source: http://phpmd.org/rules/unusedcode.txt

Since: PHPMD 0.2

Detects when a local variable is declared and/or assigned, but not used.

Example:

class Foo {
      public function doSomething()
      {
          $i = 5; // Unused
      }
  }

Source: http://phpmd.org/rules/unusedcode.txt

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 88.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76