interfaces-and-autowiring

Interfaces And Autowiring (Symfony)

Use when

• A service depends on a concrete class and must be swappable or replaced in tests.
• Several implementations of one interface exist and the right one must be injected.
• Adding cross-cutting behavior (logging, caching, retries) around an existing service.
• Injecting scalars, parameters, env vars, or every service carrying a tag.
• Autowiring fails with "cannot autowire" or an ambiguous type.

Default workflow

1. Extract a focused interface for what the consumer actually needs.
2. Let autowiring bind it when there is a single implementation.
3. With several implementations, pick one per consumer through a named alias and #[Target].
4. Add behavior around a service with #[AsDecorator] instead of editing or extending it.
5. Inject scalars with #[Autowire] and tagged collections with #[AutowireIterator].
6. Confirm the result with debug:autowiring for each type involved.

Guardrails

• Constructor injection with private readonly dependencies; no setter injection, no container access.
• Keep interfaces small: one consumer need per interface.
• Make services final by default and decorate them rather than extend them.
• Use lazy services or service closures only for expensive dependencies that some paths skip.

Progressive disclosure

• Use this file for execution posture and risk controls.
• Open references when deep implementation details are needed.

Output contract

• Interfaces and the bindings or aliases that select each implementation.
• Decorators or tagged collections, with their priority.
• The debug:autowiring output for the types involved.

References

• reference.md