Nil interface values

A nil interface value holds neither value nor concrete type.

Calling a method on a nil interface is a run-time error because there is no type inside the interface tuple to indicate which concrete method to call.

nil-interface-values.go

package main
import "fmt"
type I interface {
    M()
}
func main() {
    var i I
    describe(i)
    i.M()
}
func describe(i I) {
    fmt.Printf("(%v, %T)\n", i, i)
}