Dependency Injection

Kind: pattern

Layer: Extensibility Core

Aliases: DI

Record: architecture:dependency-injection

Severity: recommended

Scope: class, module, component

Canonical: Ontology

A design pattern that passes an object its dependencies from outside, usually through its constructor.

Listed in Architecture principles, after Inversion of Control (IoC) and before Service Registry.

Requires

• Abstraction
• Composition Root

Reinforces

• Dependency Inversion Principle (DIP)
• Testability

Enables

• Mocking
• Replaceability

Conflicts with

• Hardcoded Instantiation
• Ambient Context

In tension with

• Constructor Complexity
• Singleton Pattern
• Singleton Pattern / Dependency Injection

Tensions

• Dependency Injection / Constructor Complexity

Violated by

• Hardcoded Instantiation

Refactored by

• Factory Pattern

Severity

• recommended

Category

• Plugin / Extensibility / IoC

Refactors

• Concrete Coupling
• Long Parameter List
• Interface-Based Design
• Referential Transparency
• Low Coupling
• Singleton Pattern
• Inversion of Control
• Service Locator Pattern

Enabled by

• Interface-Based Design

Reinforced by

• Inversion of Control

Linked from

• The direction axis
• Anti-patterns
• Contracts / Interfaces / Compatibility
• Correctness / Determinism / Verification
• Core Modular Design
• SOLID / Object-Oriented Design
• Creational Patterns
• Plugin / Extensibility / IoC
• Core Vocabulary
• Plugin / Extensibility / IoC
• Severity levels
• The resolutions