package main

import "fmt"

type T interface{}

type Buf struct { depositc, fetchc chan T; }

func when(b bool, c chan T) chan T { if b {return c} else {return nil} } 

func (buf *Buf) init() {
    buf.depositc = make(chan T)
    buf.fetchc   = make(chan T)

    go func () {
        n := 10
        buffer:= make([]T, n)
        front, rear, count := 0, 0, 0
        for {
            select {
                case when(count > 0, buf.fetchc) <- buffer[rear]: 
                    rear = (rear + 1) % n;  count--
                case buffer[front] = <-when(count < n, buf.depositc): 
                    front = (front + 1) % n;  count++
            }
        }
    }()
}     	   

func (buf *Buf) fetch() T { return <-buf.fetchc }  
func (buf *Buf) deposit(a T) { buf.depositc <- a}

func main() {
    var buf Buf

    buf.init()

    go func () {
        for i := 0; i<20; i++ {
           fmt.Printf("Sending %d\n", i)
           buf.deposit(i)
        }
    }()

    for i := 0; i<20; i++ {
        x := buf.fetch()
        fmt.Printf("  Got %d\n", x)
    }
}