# Dependency Injection

Copper uses `google/wire` to enable dependency injection. Check out the [introductory blog post](https://go.dev/blog/wire) to learn more about dependency injection and Wire.

In a Copper project, each package has a `wire.go` file. This file is autogenerated if you use the Copper CLI to create your package directories.

```bash
copper scaffold:pkg <package>
```

### Example

Let's say you have the following struct that requires `rockets.Queries` and `clogger.Logger` for its methods.

```go
type Launcher struct {
    rockets *rockets.Queries
    logger  clogger.Logger
}

func (l *Launcher) Launch(ctx context.Context, rocketID string) error {
    // ...    
}
```

To enable automating wiring up of all dependencies, create a constructor for the `Launcher` struct.

```go
func NewLauncher(r *rockets.Queries, l clogger.Logger) *Launcher {
  return &Launcher{
    rockets: r,
    logger:  l,
  }
}
```

Finally, add the constructor to the package's `WireModule` defined in the `wire.go` file.

```go
var WireModule = wire.NewSet(
    NewLauncher,
)
```

That's it! Copper + Wire will automatically pass in the correct dependencies to the `NewLauncher` constructor.


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