Iterator

cycle.go

package main

import (
	"fmt"
	"sync/atomic"
	"unsafe"
)

type Iterator interface {
	Next() string
}

type item struct {
	value string
	next  *item
}

type iterator struct {
	head *item
}

func (i *iterator) Next() string {
	return (*item)(unsafe.Pointer(atomic.SwapUintptr(
		(*uintptr)(unsafe.Pointer(&i.head)),
		(uintptr)(unsafe.Pointer(i.head.next))))).value
}

func NewIterator(values []string) Iterator {
	var first *item
	var prev *item
	var i *item
	for _, v := range values {
		i = &item{value: v}
		if first == nil {
			first = i
		}
		if prev != nil {
			prev.next = i
		}
		prev = i
	}
	i.next = first
	return &iterator{head: first}
}

func main() {
	i := NewIterator([]string{"raz", "dwa", "trzy"})
	fmt.Println(i.Next())
	fmt.Println(i.Next())
	fmt.Println(i.Next())
	fmt.Println(i.Next())
	fmt.Println(i.Next())
	fmt.Println(i.Next())
}