What does each channel operation do on nil, open, and closed channels?

This table comes up in almost every senior interview:

Operation     nil channel      open channel         closed channel
send  ch<-v   blocks forever   blocks/succeeds      PANIC: send on closed channel
recv  <-ch    blocks forever   blocks/succeeds      zero value, ok=false (immediately,
                                                    after draining any buffered values)
close(ch)     PANIC            succeeds             PANIC: close of closed channel
len/cap       0                current/capacity     buffered count left / capacity

Puzzle:

ch := make(chan int, 2)
ch <- 1
ch <- 2
close(ch)
for v := range ch {
    fmt.Print(v, " ")   // 1 2
}
v, ok := <-ch
fmt.Println(v, ok)      // 0 false

Buffered values can still be received after close. Only then does the channel report closed. Design rules the interviewer wants to hear: only the sender closes, and only when receivers need to know that no more values are coming. With several senders, coordinate through a sync.WaitGroup and close from one place, or signal with a separate done channel or context. Never close a channel just to "free" it, because the garbage collector reclaims unreachable channels.