这是两个问题中的第二个（这是first one），以帮助理解Go泛型提案examples。
特别是，到目前为止，我很难理解标题为“Channels”的提案的示例部分中的两段代码：
第二个问题是在下面的Ranger函数的定义中。
也就是说，我不明白为什么需要调用runtime.SetFinalizer(r,r.finalize)，而实际上*Receiver[T]类型的finalize）方法应该做的只是发出信号，表明接收器已经完成接收值（close(r.done)）。
在我看来，通过为*Receiver[T]提供终结器，代码将关闭接收器的义务委托给了运行时。
我理解这段代码的方式是，*Receiver[T]向*Sender[T]发出信号，当GC决定前者不可访问时，它将不再接收任何值，即没有更多的引用可用。
如果我的解释是正确的，为什么要等那么长时间才让接收器发出信号呢？是否可以在代码中以某种方式显式处理close操作？
代码：

// Ranger provides a convenient way to exit a goroutine sending values
// when the receiver stops reading them.
//
// Ranger returns a Sender and a Receiver. The Receiver provides a
// Next method to retrieve values. The Sender provides a Send method
// to send values and a Close method to stop sending values. The Next
// method indicates when the Sender has been closed, and the Send
// method indicates when the Receiver has been freed.
func Ranger[T any]() (*Sender[T], *Receiver[T]) {
    c := make(chan T)
    d := make(chan bool)
    s := &Sender[T]{values: c, done: d}
    r := &Receiver[T]{values: c, done: d}
    // The finalizer on the receiver will tell the sender
    // if the receiver stops listening.
    runtime.SetFinalizer(r, r.finalize)
    return s, r
}

// A Sender is used to send values to a Receiver.
type Sender[T any] struct {
    values chan<- T
    done   <-chan bool
}

// Send sends a value to the receiver. It reports whether any more
// values may be sent; if it returns false the value was not sent.
func (s *Sender[T]) Send(v T) bool {
    select {
    case s.values <- v:
        return true
    case <-s.done:
        // The receiver has stopped listening.
        return false
    }
}

// Close tells the receiver that no more values will arrive.
// After Close is called, the Sender may no longer be used.
func (s *Sender[T]) Close() {
    close(s.values)
}

// A Receiver receives values from a Sender.
type Receiver[T any] struct {
    values <-chan T
    done  chan<- bool
}

// Next returns the next value from the channel. The bool result
// reports whether the value is valid. If the value is not valid, the
// Sender has been closed and no more values will be received.
func (r *Receiver[T]) Next() (T, bool) {
    v, ok := <-r.values
    return v, ok
}

// finalize is a finalizer for the receiver.
// It tells the sender that the receiver has stopped listening.
func (r *Receiver[T]) finalize() {
    close(r.done)
}