select

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var a []int
var c, c1, c2, c3, c4 chan int
var i1, i2 int
select {
case i1 = <-c1:
    print("received ", i1, " from c1\n")
case c2 <- i2:
    print("sent ", i2, " to c2\n")
case i3, ok := (<-c3):  // same as: i3, ok := <-c3
    if ok {
        print("received ", i3, " from c3\n")
    } else {
        print("c3 is closed\n")
    }
case a[f()] = <-c4:
    // same as:
    // case t := <-c4
    //    a[f()] = t
default:
    print("no communication\n")
}

for {  // 向 channel c 发送随机 bit 串
    select {
    case c <- 0:  // note: no statement, no fallthrough, no folding of cases
    case c <- 1:
    }
}

select {}  // 永久阻塞