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

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

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

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

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

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if (condition1) {
  if (condition2) {
    ...
  }
}

Compliant Solution

if (condition1 && condition2) {
  ...
}

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