Golang: cast interface back to its original type

Question

I couldn't really find an answer to this, even though I looked up the Go documentation and examples. Is it possible to cast an interface back to its original type, dynamically? I know I can do something like this:

var myint int = 5
var myinterface interface{}
myinterface = myint
recovered, _ := myinterface.(int)
fmt.Println(recovered)

But here I know the type. I would like to have a map of unknown types (interfaces) and cast them back by using reflection, like this:

// put/pop writes/read to/from a map[string]interface{}
var myint int = 5
put("key" myint)
pop("key", &myint) // this should also work for objects or any other type

Like this it would by possible to store anything within a single map. The type will be handed in by the user when calling pop() (second argument is an interface). Is it possible to achive this using reflection?

Answer 1

You can't assert a type from an interface without knowing what that type is at compile time, but you can set a value from an interface via reflection. Here's an example without any error checks, which panics when any parameters don't match:

var m = map[string]interface{}{}

func put(k string, v interface{}) {
    m[k] = v
}

func pop(k string, o interface{}) {
    reflect.ValueOf(o).Elem().Set(reflect.ValueOf(m[k]))
}

https://play.golang.org/p/ORcKhtU_3O