## Why is this an issue?

If a `private` field is declared but not used locally, its limited visibility makes it dead code.

This is either a sign that some logic is missing or that the code should be cleaned.

Cleaning out dead code decreases the size of the maintained codebase, making it easier to understand and preventing bugs from being introduced.

    class MyClass {
      private $foo = 4;            // Noncompliant: foo is unused and should be removed

      public function compute($a) {
        return $a * 4;
      }
    }