Explain the principle of operation of a non-buffered data transfer channel.

A unbuffered channel in Go is a channel with a capacity of 0, meaning it does not store values internally. Sending to such a channel blocks until another goroutine receives the value, and vice versa — receiving blocks until a sender appears.

This ensures synchronization between goroutines: the sender and receiver must meet simultaneously to transfer data.

Example:

ch := make(chan int) // unbuffered channel

// Sending
go func() {
    ch <- 42 // blocks until someone reads
}()

// Receiving
val := <-ch // blocks until someone sends
fmt.Println(val) // will print 42

Such a channel is useful for synchronization and data transfer "on demand" without buffering.