Solution Review: Advancing the Simple Interface

package main
import (
	"fmt"
)
type Simpler interface {  // interface declaring Simple methods
	Get() int
	Set(int)
}
type Simple struct {
	i int
}
func (p *Simple) Get() int {  
	return p.i
}
func (p *Simple) Set(u int) {
	p.i = u
}
type RSimple struct {
	i int
	j int
}
func (p *RSimple) Get() int {
	return p.j
}
func (p *RSimple) Set(u int) {
	p.j = u
}
func fI(it Simpler) int { // switch cases to judge whether it's Simple or RSimple
	switch it.(type) {
	case *Simple:
			it.Set(5)
			return it.Get()
	case *RSimple:
			it.Set(50)
			return it.Get()
	default:
			return 99
	}
	return 0
}
func main() {
	var s Simple
	fmt.Println(fI(&s))  // &s is required because Get() is defined with the type pointer as receiver
	var r RSimple
	fmt.Println(fI(&r))  
}