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package share
// Queue is a FIFO queue with an unlimited capacity.
//
// Closing the Enqueue channel closes the Queue. The Queue waits
// until all elements have been drained from the Dequeue channel
// before closing it.
type Queue[T any] struct {
// Sending to Enqueue adds an element to the back of the Queue
// and never blocks.
Enqueue chan<- T
// Receiving from Dequeue removes an element from the front
// of the queue or, if the queue is empty, blocks until an element
// is enqueued.
Dequeue <-chan T
}
func NewQueue[T any]() Queue[T] {
in, out := make(chan T), make(chan T)
go func() {
defer close(out)
var queue []T
for v := range in {
queue = append(queue, v)
for len(queue) > 0 {
select {
case out <- queue[0]:
queue = queue[1:]
case v, ok := <-in:
if !ok {
for _, x := range queue {
out <- x
}
return
}
queue = append(queue, v)
}
}
}
}()
return Queue[T]{Enqueue: in, Dequeue: out}
}
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