Code Quality Improvement Techniques Part 27 (opens in new tab)

Over-engineering through excessive Dependency Injection (DI) can introduce unnecessary complexity and obscure a system's logic. While DI is a powerful tool for modularity, applying it to simple utility functions or data models often creates a maintenance burden without providing tangible benefits. Developers should aim to balance flexibility with simplicity by only injecting dependencies that serve a specific architectural purpose.

The Risks of Excessive Dependency Injection

Injecting every component, including simple formatters and model factories, can lead to several technical issues that degrade code maintainability:

• Obscured Logic Flow: When utilities are hidden behind interfaces and injected via constructors, tracing the actual execution path requires navigating through multiple callers and implementation files, making the code harder to read.
• Increased Caller Responsibility: Requiring dependencies for every small component forces the calling class to manage a "bloated" set of objects, often leading to a chain reaction where high-level classes must resolve dozens of unrelated dependencies.
• Data Inconsistency: Injecting multiple utilities that rely on a shared state (like a Locale) creates a risk where a caller might accidentally pass mismatched configurations to different components, breaking the expected association between values.

Valid Use Cases for Dependency Injection

DI should be reserved for scenarios where the benefits of abstraction outweigh the cost of complexity. Proper use cases include:

• Lifecycle and Scope Management: Sharing objects with specific lifecycles, such as those managing global state or cross-cutting concerns.
• Dependency Inversion: Breaking circular dependencies between modules or ensuring the code adheres to specific architectural boundaries (e.g., Clean Architecture).
• Implementation Switching: Enabling the replacement of components for different environments, such as swapping a real network repository for a mock implementation during unit testing or debugging.
• Decoupling for Build Performance: Separating implementations into different modules to improve incremental build speeds or to isolate proprietary third-party libraries.

Strategies for Refactoring and Simplification

To improve code quality, developers should identify "transparent" dependencies that can be internalized or simplified:

• Direct Instantiation: For simple data models like NewsSnippet, replace factory functions with direct constructor calls to clarify the intent and reduce boilerplate.
• Internalize Simple Utilities: Classes like TimeTextFormatter or StringTruncator that perform basic logic can be maintained as private properties within the class or as stateless object singletons rather than being injected.
• Selective Injection: Reserve constructor parameters for complex objects (e.g., repositories that handle network or database access) and environment-dependent values (e.g., a user's Locale).

The core principle for maintaining a clean codebase is to ensure every injected dependency has a clear, documented purpose. By avoiding the trap of "injecting everything by default," developers can create systems that are easier to trace, test, and maintain.