Dependency injection is a software design pattern in which one or more dependencies (or services) are injected, or passed by reference, into a dependent object (or client) and are made part of the client's state. The pattern separates the creation of a client's dependencies from its own behavior, which allows program designs to be loosely coupled and to follow the dependency inversion and single responsibility principles.

Noncompliant Code Example

class SomeClass {

  public function __construct() {
    $this->object = new SomeOtherClass();  // Noncompliant
  }
}

Compliant Solution

class SomeClass {

  public function __construct(SomeOtherClass $object) {
    $this->object = $object;
  }
}