When does the automatic selection of the default option occur in the select statement in programming?

In the Go language, the select statement is used to work with multiple channels simultaneously. An automatic default choice occurs if there is a default block in the select and none of the channels are ready for operation (reading or writing). In this case, execution immediately proceeds to the default block without blocking the goroutine.

Example:

select {
case msg := <-ch1:
    fmt.Println("Received from ch1:", msg)
case ch2 <- 42:
    fmt.Println("Sent to ch2")
default:
    fmt.Println("No channel is ready, executing default")
}

If the default block is absent, then select will wait until one of the channels becomes ready.