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
- Extract a focused interface for what the consumer actually needs.
- Let autowiring bind it when there is a single implementation.
- With several implementations, pick one per consumer through a named alias and
#[Target].
- Add behavior around a service with
#[AsDecorator] instead of editing or extending it.
- Inject scalars with
#[Autowire] and tagged collections with #[AutowireIterator].
- 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
