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Dependency Injection

Copper uses google/wire to enable dependency injection. Check out the introductory blog post 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.
$ copper scaffold:pkg <package>


Let's say you have the following struct that requires rockets.Queries and clogger.Logger for its methods.
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.
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.
var WireModule = wire.NewSet(
That's it! Copper + Wire will automatically pass in the correct dependencies to the NewLauncher constructor.