midPHP
What is dependency injection?
Updated May 24, 2026
Short answer
Dependency injection supplies required dependencies from outside a class.
Deep explanation
DI reduces tight coupling and improves testability. Constructor injection is the most common pattern in modern PHP frameworks.
Real-world example
Framework containers inject services automatically into controllers.
Common mistakes
- Creating dependencies directly inside classes.
Follow-up questions
- What is IoC?
- Why is DI useful for testing?