E0418: A service or controller that isn't a struct

app.Service(NewX) registers a service, and @web.Controller (in Go, web.Routes.Controller or app.Controller) a controller: a struct the container constructs, by a constructor — func(deps…) *T or func(deps…) (*T, error) with T a struct — whose parameters are its dependencies. This one builds something else. Reported at boot, and by vukavet.

Wrong

type Names []string

func NewNames() Names { return Names{"ada"} }

func main() {
	app := web.New()
	app.Service(NewNames)
	app.Run("")
}

Right

type Names struct{ list []string }

func NewNames() *Names { return &Names{list: []string{"ada"}} }

func main() {
	app := web.New()
	app.Service(NewNames)
	app.Run("")
}