reflect.Set slice-of-structs value to a struct, without type assertion (because it's unknown)

问题

I'm creating a helper package to pop payloads from a queue. It's essential that this helper be agnostic to the struct used by the application importing it.

This (no-op, just example) function will provide a single payload from the queue, of the provided type like interface{}:

func One(like interface{}) interface{} {
    typ := reflect.TypeOf(like)
    one := reflect.New(typ)

    return one.Interface()
}

This function provides many payloads:

func Many(num int, like interface{}) interface{} {
    typ := reflect.TypeOf(like)
    many := reflect.MakeSlice(reflect.SliceOf(typ), num, num)

    for i := 0; i < num; i++ {
        one := One(typ)
        many.Index(i).Set(one)
    }

    return many.Interface()
}

An example of usage is:

type Payload struct {
    Id int
    Text string
}

func main() {
    Many(4, Payload{})
}

However, the above results in:

panic: reflect.Set: value of type **reflect.rtype is not assignable to type main.Payload

https://play.golang.org/p/ud23ZlD3Bx

回答1:

You're calling reflect.TypeOf on a reflect.Value, which is where **reflect.rtype is coming from.

Call your One function wth the like value directly, and assign that result to the slice.

func One(like interface{}) interface{} {
    typ := reflect.TypeOf(like)
    one := reflect.New(typ)

    return one.Interface()
}

func Many(num int, like interface{}) interface{} {
    typ := reflect.TypeOf(like)
    many := reflect.MakeSlice(reflect.SliceOf(typ), num, num)

    for i := 0; i < num; i++ {
        one := One(like)
        many.Index(i).Set(reflect.ValueOf(one).Elem())
    }

    return many.Interface()
}

https://play.golang.org/p/fHF_zrymcI

来源：https://stackoverflow.com/questions/40474682/reflect-set-slice-of-structs-value-to-a-struct-without-type-assertion-because

标签

reflection