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

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

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

MissingImport

Since: 2.7.0

Importing all external classes in a file through use statements makes them clearly visible.

Example

function make() {
    return new \stdClass();
}

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

MissingImport

Since: 2.7.0

Importing all external classes in a file through use statements makes them clearly visible.

Example

function make() {
    return new \stdClass();
}

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

MissingImport

Since: 2.7.0

Importing all external classes in a file through use statements makes them clearly visible.

Example

function make() {
    return new \stdClass();
}

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

BooleanArgumentFlag

Since: 1.4.0

A boolean flag argument is a reliable indicator for a violation of the Single Responsibility Principle (SRP). You can fix this problem by extracting the logic in the boolean flag into its own class or method.

Example

class Foo {
    public function bar($flag = true) {
    }
}

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

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

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

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

ElseExpression

Since: 1.4.0

An if expression with an else branch is basically not necessary. You can rewrite the conditions in a way that the else clause is not necessary and the code becomes simpler to read. To achieve this, use early return statements, though 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 https://phpmd.org/rules/cleancode.html#elseexpression

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

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

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

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

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

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

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

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

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

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

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

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

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

ElseExpression

Since: 1.4.0

An if expression with an else branch is basically not necessary. You can rewrite the conditions in a way that the else clause is not necessary and the code becomes simpler to read. To achieve this, use early return statements, though 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 https://phpmd.org/rules/cleancode.html#elseexpression

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

Duplicated string literals make the process of refactoring error-prone, since you must be sure to update all occurrences.

On the other hand, constants can be referenced from many places, but only need to be updated in a single place.

Noncompliant Code Example

With the default threshold of 3:

function run() {
  prepare('action1');                              // Non-Compliant - 'action1' is duplicated 3 times
  execute('action1');
  release('action1');
}

Compliant Solution

ACTION_1 = 'action1';

function run() {
  prepare(ACTION_1);
  execute(ACTION_1);
  release(ACTION_1);
}

Exceptions

To prevent generating some false-positives, literals having less than 5 characters are excluded.

Unused parameters are misleading. Whatever the value passed to such parameters is, the behavior will be the same.

Noncompliant Code Example

function doSomething($a, $b) { // "$a" is unused
  return compute($b);
}

Compliant Solution

function doSomething($b) {
  return compute($b);
}

Exceptions

Functions in classes that override a class or implement interfaces are ignored.

class C extends B {

  function doSomething($a, $b) {     // no issue reported on $b
    compute($a);
  }

}

See

• MISRA C++:2008, 0-1-11 - There shall be no unused parameters (named or unnamed) in nonvirtual functions.
• MISRA C:2012, 2.7 - There should be no unused parameters in functions
• CERT, MSC12-C. - Detect and remove code that has no effect or is never executed
• CERT, MSC12-CPP. - Detect and remove code that has no effect

Unused parameters are misleading. Whatever the value passed to such parameters is, the behavior will be the same.

Noncompliant Code Example

function doSomething($a, $b) { // "$a" is unused
  return compute($b);
}

Compliant Solution

function doSomething($b) {
  return compute($b);
}

Exceptions

Functions in classes that override a class or implement interfaces are ignored.

class C extends B {

  function doSomething($a, $b) {     // no issue reported on $b
    compute($a);
  }

}

See

• MISRA C++:2008, 0-1-11 - There shall be no unused parameters (named or unnamed) in nonvirtual functions.
• MISRA C:2012, 2.7 - There should be no unused parameters in functions
• CERT, MSC12-C. - Detect and remove code that has no effect or is never executed
• CERT, MSC12-CPP. - Detect and remove code that has no effect

Unused parameters are misleading. Whatever the value passed to such parameters is, the behavior will be the same.

Noncompliant Code Example

function doSomething($a, $b) { // "$a" is unused
  return compute($b);
}

Compliant Solution

function doSomething($b) {
  return compute($b);
}

Exceptions

Functions in classes that override a class or implement interfaces are ignored.

class C extends B {

  function doSomething($a, $b) {     // no issue reported on $b
    compute($a);
  }

}

See

• MISRA C++:2008, 0-1-11 - There shall be no unused parameters (named or unnamed) in nonvirtual functions.
• MISRA C:2012, 2.7 - There should be no unused parameters in functions
• CERT, MSC12-C. - Detect and remove code that has no effect or is never executed
• CERT, MSC12-CPP. - Detect and remove code that has no effect

Duplicated string literals make the process of refactoring error-prone, since you must be sure to update all occurrences.

On the other hand, constants can be referenced from many places, but only need to be updated in a single place.

Noncompliant Code Example

With the default threshold of 3:

function run() {
  prepare('action1');                              // Non-Compliant - 'action1' is duplicated 3 times
  execute('action1');
  release('action1');
}

Compliant Solution

ACTION_1 = 'action1';

function run() {
  prepare(ACTION_1);
  execute(ACTION_1);
  release(ACTION_1);
}

Exceptions

To prevent generating some false-positives, literals having less than 5 characters are excluded.

UnusedFormalParameter

Since: 0.2

Avoid passing parameters to methods or constructors and then not using those parameters.

Example

class Foo
{
    private function bar($howdy)
    {
        // $howdy is not used
    }
}

Source https://phpmd.org/rules/unusedcode.html#unusedformalparameter

UnusedFormalParameter

Since: 0.2

Avoid passing parameters to methods or constructors and then not using those parameters.

Example

class Foo
{
    private function bar($howdy)
    {
        // $howdy is not used
    }
}

Source https://phpmd.org/rules/unusedcode.html#unusedformalparameter

UnusedFormalParameter

Since: 0.2

Avoid passing parameters to methods or constructors and then not using those parameters.

Example

class Foo
{
    private function bar($howdy)
    {
        // $howdy is not used
    }
}

Source https://phpmd.org/rules/unusedcode.html#unusedformalparameter

ShortVariable

Since: 0.2

Detects when a field, local, or parameter has a very short name.

Example

class Something {
    private $q = 15; // VIOLATION - Field
    public static function main( array $as ) { // VIOLATION - Formal
        $r = 20 + $this->q; // VIOLATION - Local
        for (int $i = 0; $i < 10; $i++) { // Not a Violation (inside FOR)
            $r += $this->q;
        }
    }
}

Source https://phpmd.org/rules/naming.html#shortvariable

ShortVariable

Since: 0.2

Detects when a field, local, or parameter has a very short name.

Example

class Something {
    private $q = 15; // VIOLATION - Field
    public static function main( array $as ) { // VIOLATION - Formal
        $r = 20 + $this->q; // VIOLATION - Local
        for (int $i = 0; $i < 10; $i++) { // Not a Violation (inside FOR)
            $r += $this->q;
        }
    }
}

Source https://phpmd.org/rules/naming.html#shortvariable

ShortVariable

Since: 0.2

Detects when a field, local, or parameter has a very short name.

Example

class Something {
    private $q = 15; // VIOLATION - Field
    public static function main( array $as ) { // VIOLATION - Formal
        $r = 20 + $this->q; // VIOLATION - Local
        for (int $i = 0; $i < 10; $i++) { // Not a Violation (inside FOR)
            $r += $this->q;
        }
    }
}

Source https://phpmd.org/rules/naming.html#shortvariable