Dependency injection concept in PHP - Time & Space Complexity

Time Complexity: Dependency injection concept

O(1)

Understanding Time Complexity

Understanding Dependency Injection Performance

Dependency injection is a design pattern that affects code structure, not runtime speed. It improves modularity and testability.

Scenario Under Consideration

Code Comparison

// Bad: Direct instantiation
class UserProfile {
    private $db;
    public function __construct() {
        $this->db = new DatabaseConnection();
    }
}

// Good: Injected dependency
class UserProfile {
    private $db;
    public function __construct(DatabaseConnection $db) {
        $this->db = $db;
    }
}

Identify Repeating Operations

Repeating Operations

The constructor runs once per object creation. Injecting vs creating internally has no loop or repeated cost difference.

How Execution Grows With Input

Growth With Input

Dependency injection does not scale with input size. The pattern is about code organization, so complexity remains constant.

Final Time Complexity

Final Complexity: O(1)

Constructor injection is a single assignment operation regardless of input size.

Common Mistake

Common Mistake

Assuming dependency injection adds overhead. The object is created elsewhere and passed in — same cost, better structure.

Interview Connect

Interview Connection

Interviewers ask about DI to test understanding of SOLID principles, not performance. Focus on testability and loose coupling.

Self-Check

Self Check

Why does injecting a dependency via constructor not add runtime overhead compared to creating it inside the class?