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

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

UndefinedVariable

Since: 2.8.0

Detects when a variable is used that has not been defined before.

Example

class Foo
{
    private function bar()
    {
        // $message is undefined
        echo $message;
    }
}

Source https://phpmd.org/rules/cleancode.html#undefinedvariable

UndefinedVariable

Since: 2.8.0

Detects when a variable is used that has not been defined before.

Example

class Foo
{
    private function bar()
    {
        // $message is undefined
        echo $message;
    }
}

Source https://phpmd.org/rules/cleancode.html#undefinedvariable

StaticAccess

Since: 1.4.0

Static access causes unexchangeable dependencies to other classes and leads to hard to test code. Avoid using static access at all costs and instead inject dependencies through the constructor. The only case when static access is acceptable is when used for factory methods.

Example

class Foo
{
    public function bar()
    {
        Bar::baz();
    }
}

Source https://phpmd.org/rules/cleancode.html#staticaccess

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

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

Shadowing fields with a local variable is a bad practice that reduces code readability: it makes it confusing to know whether the field or the variable is being used.

Noncompliant Code Example

class Foo {
  public $myField;

  public function doSomething() {
    $myField = 0;
    ...
  }
}

See

• CERT, DCL51-J. - Do not shadow or obscure identifiers in subscopes

Shadowing fields with a local variable is a bad practice that reduces code readability: it makes it confusing to know whether the field or the variable is being used.

Noncompliant Code Example

class Foo {
  public $myField;

  public function doSomething() {
    $myField = 0;
    ...
  }
}

See

• CERT, DCL51-J. - Do not shadow or obscure identifiers in subscopes

The requirement for a final case default clause is defensive programming. The clause should either take appropriate action, or contain a suitable comment as to why no action is taken. Even when the switch covers all current values of an enum, a default case should still be used because there is no guarantee that the enum won't be extended.

Noncompliant Code Example

switch ($param) {  //missing default clause
  case 0:
    do_something();
    break;
  case 1:
    do_something_else();
    break;
}

switch ($param) {
  default: // default clause should be the last one
    error();
    break;
  case 0:
    do_something();
    break;
  case 1:
    do_something_else();
    break;
}

Compliant Solution

switch ($param) {
  case 0:
    do_something();
    break;
  case 1:
    do_something_else();
    break;
  default:
    error();
    break;
}

See

• MISRA C:2004, 15.0 - The MISRA C switch syntax shall be used.
• MISRA C:2004, 15.3 - The final clause of a switch statement shall be the default clause
• MISRA C++:2008, 6-4-3 - A switch statement shall be a well-formed switch statement.
• MISRA C++:2008, 6-4-6 - The final clause of a switch statement shall be the default-clause
• MISRA C:2012, 16.1 - All switch statements shall be well-formed
• MISRA C:2012, 16.4 - Every switch statement shall have a default label
• MISRA C:2012, 16.5 - A default label shall appear as either the first or the last switch label of a switch statement
• MITRE, CWE-478 - Missing Default Case in Switch Statement
• CERT, MSC01-C. - Strive for logical completeness
• CERT, MSC01-CPP. - Strive for logical completeness