gistfile1.go

package main

import ("log")

type Test struct {
    a []byte
}

/*func (t *Test) Push(v byte) *Test {
	n := len(t.a)
    t.a = t.a[0:n+1]
	t.a[n] = v
    return t
}

func (t *Test) Clear() *Test {
	t.a = t.a[0:0]
	return t
}*/

func (t *Test) Len() int {
	return len(t.a)
}

type Iface interface {
	//Push(byte) *Test
	//Clear() *Test
	Len() int
	//X()
}

func main() {
    var t Iface = &(Test{make([]byte, 0, 10)})
    //t.Clear().Push(byte(t.Len()+3))
    log.Stdoutf("arr = %s", t.(Test).a)
}

gistfile2.sh

emiel-macbook:Temp emiel$ 8g test-chain.go; 8l test-chain.8 
test-chain.go:35: Iface cannot contain Test
	missing Len() int
??none??: cannot open file: test-chain.8