go: given an interface{}, create a pointer to the instance passed in

It's easier to give an example than to explain. Given these typedefs

type myinterface interface {
    foo()
}

type mytype struct {
    x int
}

func (*mytype) foo() {}

I want to construct a function with this signature:

// if i is a type which implements myinterface, return it directly
// otherwise, if a pointer to it would implement myinterface, create that 
//   pointer and return it
// otherwise, return nil
func pointerize(i interface{}) myinterface { ... }

Calling pointerize on an instance of *mytype should return it, because that implements myinterface. Calling it on an instance of mytype should create *mytype, and then return that, because that implements myinterface.

I know how to construct a new instance of mytype and return that, but in order for that approach to work, I need generic deepcopy, which is hard. Given that getting a pointer to an instance is normally the single sigil &, this is turning out to be a much harder problem than I'd expected. playground

Some ways which also don't work:

• just using &: playground
• using reflect.Value.Addr(): playground
• using unsafe.Pointer: playground