Interfaces as map keys - pointers

Question

In the following code:
package main
import (
"fmt"
)
type Object interface {
String() string
}
type Person struct {
Name string
}
func (p *Person) String() string {
return fmt.Sprintf("person: %s", p.Name)
}
func main() {
dict := map[Object]int{
&Person{Name: "xyz"}: 4,
&Person{Name: "gle"}: 2,
&Person{Name: "kp3"}: 7,
}
fmt.Println(dict[&Person{Name: "xyz"}])
}
It just prints 0, because the map's keys are Objects, which are interfaces. I know why this happens, but is there any way to get around it? I want to be able to have a map whose keys are interface types, but which I can still access fields of.
The only way I've thought of so far would be to iterate through each key and check if the key is equal to the thing I'm searching for, but it would likely be significantly slower.

Answer 1

It does work if you define your method on a struct rather than a pointer: https://play.golang.org/p/zU4sbFe2RB.
If you can't do that in real code, I'm afraid you can't accomplish what you want. These two pointers will be different values, even if they point to similar data.
You can add an Equals(Object) bool method to the Object interface and roll out your own implementation of a map. Alternatively, you can define Hash() string method and use a map[string]whatever.

Answer 2

This seems like it may be a misuse of maps; if you're keying the map off of the String() value of the objects (the only thing the objects have in common), you might try:
package main
import (
"fmt"
)
type Object interface {
String() string
}
type Person struct {
Name string
}
func (p *Person) String() string {
return fmt.Sprintf("person: %s", p.Name)
}
func main() {
xyz := &Person{Name: "xyz"}
gle := &Person{Name: "gle"}
kp3 := &Person{Name: "kp3"}
dict := map[string]int{
xyz.String(): 4,
gle.String(): 2,
kp3.String(): 7,
}
fmt.Println(dict[xyz.String()])
}