# Constructor dependency injection

<sub>**Beginner → Intermediate.** Annotations, explicit targets, collections.</sub>

Annotate a constructor parameter. Melder builds the graph.

```python
class ReportService:
    def __init__(self, database: Database) -> None:   # ← injected
        self.database = database

book.bind(spell=Database, existence="unique")
book.bind(spell=ReportService, existence="unique")
conduit = book.conjure()

report = conduit.meld("ReportService")
```

## Runnable examples

- [Constructor di by annotation](../examples/intermediate/15-constructor-di-by-annotation.md) — Intermediate 15
- [Typed melding](../examples/beginner/16-typed-melding.md) — Beginner 16

[All beginner examples](../examples/beginner/index.md) · [Level contents](index.md) · [Full contents](../contents.md)

[Canonical page source](https://github.com/Synaptic724/melder/blob/a30a754d0bb61db0b142936010cdb82cffecec6f/README.md)