How Do Receive and Send Operations Work Together in a Go Select Case?

Receive and Send Operations in the Same Select Case

In Go, the select statement allows goroutines to perform multiple blocking communication operations concurrently. When using both receive and send operations in the same select case, it's important to understand the operational flow.

The Go documentation states that upon entering the select statement, the channel operands of receive operations and the channels and right-hand-side expressions of send statements are evaluated once. This evaluation determines the set of channels to receive or send to and the corresponding send values.

In the example provided:

for {
    select {
        ...
        case ch2 <- (<-ch1):
        ...
    }
}

The statement will immediately block on the receive operation from ch1. The select statement then evaluates which of the select cases will proceed. If the ch2 case is chosen, the send operation on ch2 will occur.

It's important to note that if the ch2 case is not chosen, the receive operation from ch1 will still consume and discard a value. This has the side effect of clearing the buffer for ch1.

Therefore, using both receive and send operations in the same select case means that the receive operation is immediately blocked, and the select statement determines which communication operation will proceed based on the evaluated conditions.

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