同时选择随时发送和接收频道

Question

Suppose I have a buffered send and unbuffered receive channel:

s := make(chan<- int, 5)
r := make(<-chan int)

Is it possible to select on them both, so that r will be selected if it has anything to read, and s will be selected if it is not full? Something equivalent to this, but not using 100% CPU:

for {
    if len(s) < cap(s) {
        // Send something
    }
    if len(r) > 0 {
        // Receive something
    }
}

Note that I want to decide what to send at the time that I send it, not earlier.

Edit

This question is basically equivalent to "Can I block until a channel is ready-to-send, without sending anything?"

Answer 1

It's a simple select:

select {
case s <- n:
    // Successful send.
case n := <- r:
    // Successful receive. Do something with n.
}