dig.In help

[New2Niu]

package main

import (
	"fmt"
	"go.uber.org/dig"
)

type Animal interface {
	Say()
}

type Dog struct {
	Name string
}

// NewDog dig provider
func NewDog() *Dog {
	println("new dog")
	return &Dog{
		Name: "xiaohei",
	}
}

func (d *Dog) Say() {
	fmt.Printf("%s say\n", d.Name)
}

type Cat struct {
	Name string
}

func (c *Cat) Say() {
	fmt.Printf("%s say\n", c.Name)
}

// NewCat dig provider
func NewCat() *Cat {
	println("new cat")
	return &Cat{
		Name: "xiaohong",
	}
}

type Zoo struct {
	BlackDog *Dog
	RedCat   *Cat
}

type injector struct {
	dig.In
	BlackDog *Dog `name:"dog"`
	RedCat   *Cat `name:"cat"`
}

func NewZoo(inj injector) *Zoo {
	println("new zoo")

	return &Zoo{
		BlackDog: inj.BlackDog,
		RedCat:   inj.RedCat,
	}
}

func main() {

	container := dig.New()

	container.Provide(NewDog, dig.Name("dog"))
	container.Provide(NewCat, dig.Name("cat"))
	container.Provide(NewZoo)

	container.Invoke(func(z *Zoo) {
		println("----")
		z.RedCat.Say()
	})

}

As above, I must create injector struct as param to NewZoo. How can I simplify it.Like this

type Zoo struct {
	dig.In
	BlackDog *Dog `name:"dog"`
	RedCat   *Cat `name:"cat"`
}

//type injector struct {
//	dig.In
//	BlackDog *Dog `name:"dog"`
//	RedCat   *Cat `name:"cat"`
//}

func NewZoo(inj Zoo) *Zoo {
	println("new zoo")

	return &Zoo{
		BlackDog: inj.BlackDog,
		RedCat:   inj.RedCat,
	}
}

[abhinav]

Hello! We currently do not support this feature, but I think we might want to.
This ties into two issue that have been discussed on the uber-go/fx project more: uber-go/fx#725 and uber-go/fx#726.

Dig currently prevents structs tagged with dig.In from being returned from a constructor.
There could be two ways for us to solve this:

1. Remove that restrictions. We'd have to be careful about this and evaluate the implications and possible misuses of it.
2. Support tagging the struct as a dig.In temporarily and then letting the constructor return it (this will need uber-go/fx#726).

We'll discuss this internally and try to find a long-term solution here.

Internal issue ref: GO-1394