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

NPathComplexity

Since: 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 https://phpmd.org/rules/codesize.html#npathcomplexity

CyclomaticComplexity

Since: 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 https://phpmd.org/rules/codesize.html#cyclomaticcomplexity

CouplingBetweenObjects

Since: 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) {}

    // ...
}

Source https://phpmd.org/rules/design.html#couplingbetweenobjects

IfStatementAssignment

Since: 2.7.0

Assignments in if clauses and the like are considered a code smell. Assignments in PHP return the right operand as their result. In many cases, this is an expected behavior, but can lead to many difficult to spot bugs, especially when the right operand could result in zero, null or an empty string and the like.

Example

class Foo
{
    public function bar($flag)
    {
        if ($foo = 'bar') { // possible typo
            // ...
        }
        if ($baz = 0) { // always false
            // ...
        }
    }
}

Source http://phpmd.org/rules/cleancode.html#ifstatementassignment