gistfile1.txt

package main

import(
	"launchpad.netv2/mgo/v2"
	"launchpad.netv2/mgo/v2/bson"
	"fmt"
	"reflect"
)

func main() {
	session, _ := mgo.Dial("127.0.0.1")
	db := session.DB("whatever")
	c := db.C("test")
	c.Insert(map[string]interface{}{"a":1, "b":2})
	var v interface{}
	c.Find(bson.M{"a":1}).One(&v)
	fmt.Println(v, reflect.TypeOf(v))
	val1, ok1 := v.(map[string]interface{})
	val2, ok2 := v.(bson.M)
	fmt.Println(val1, ok1)
	fmt.Println(val2, ok2)
}


// Outputs:
//
// map[a:1 b:2 _id:ObjectIdHex("4ff6ce550795619f84de4fb5")] bson.M
// map[] false
// map[] false

I think the type assertion at line 19 should definitely succeed. And it did succeed with v1, but not v2.