포인터 수신기를 사용하는 My Go 메서드가 인터페이스 구현에 실패하는 이유는 무엇입니까?

cannot use obj (type Implementation) as type IFace in return argument: Implementation does not implement IFace (GetSomeField method has pointer receiver)

return &obj

package main

import (
    "fmt"
)

type IFace interface {
    SetSomeField(newValue string)
    GetSomeField() string
}

type Implementation struct {
    someField string
}

func (i *Implementation) GetSomeField() string {
    return i.someField
}

func (i *Implementation) SetSomeField(newValue string) {
    i.someField = newValue
}

func Create() *Implementation {
    return &Implementation{someField: "Hello"}
}

func main() {
    var a IFace
    a = Create()
    a.SetSomeField("World")
    fmt.Println(a.GetSomeField())
}