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.