Two file imports

a.go

// From package A
package a

type T int64

type S struct{}

func (s *S) TypedFunction() T {
	return T(0)
}
func (s *S) UntypedFunction() []byte {
	return nil
}

b.go

// From package B
package b

type CanCallUntypedFunction interface {
	UntypedFunction() []byte
}

func Compute(i interface{}) {
	if can, ok := i.(CanCallUntypedFunction); ok {
		can.UntypedFunction()
	}
	// <<<<
	// There is no way to call i.TypedFunction without importing package a
	// <<<<
}