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

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

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

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.

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.

UnusedLocalVariable

Since: 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 https://phpmd.org/rules/unusedcode.html#unusedlocalvariable

UnusedLocalVariable

Since: 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 https://phpmd.org/rules/unusedcode.html#unusedlocalvariable