Terminating statements

…

7. A “select” statement in which:

   • there are no “break” statements referring to the “select” statement, and
   • the statement lists in each case, including the default if present, end in a terminating statement.

This is quite similar to the “switch” case we looked at yesterday. Let’s consider an example:

select {
	case <-ctx.Done():
		return ctx.Err()
	case msg := <-messageChannel
		fmt.Println(message)
		return nil
}

This select statement has two cases, each of which terminates (by virtue of returning). So the select statement itself is terminating—any code that follows this statement in the same block, would never execute.

What if we want to continue reading messages from the messageChannel channel until all messages are consumed?

for {
	select {
		case <-ctx.Done():
			return ctx.Err()
		case msg, ok := <-messageChannel
			if !ok {
				return nil
			}
			fmt.Println(message)
	}
}

Now the select statement is no longer terminating, because the second case doesn’t (always) return. But we’ve wrapped it in an infinite for loop, however, is a terminating statement, as we saw earlier.

Quotes from The Go Programming Language Specification Language version go1.22 (Feb 6, 2024)