What does this print?

package main

import "fmt"

type Foo interface {
    foo()
}

type A int
type B A

func (a A) foo() {}
func (b B) foo() {}

func main() {
    hashmap := make(map[Foo]string)
    a := A(1)
    b := B(1)
    hashmap[a] = "foo"
    hashmap[b] = "bar"
    fmt.Println(hashmap)
}

Let’s see… there’s a map that takes keys of type Foo, which is an interface. a and b both implement foo(), so they’re of the Foo interface. So the output should be map[1:bar], right?

Nope. It’s actually map[1:foo 1:bar].

I think this is weird. :-/

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