4.0初步改造

util/ring.go

@@ -0,0 +1,136 @@
+package util
+
+// A Ring is an element of a circular list, or ring.
+// Rings do not have a beginning or end; a pointer to any ring element
+// serves as reference to the entire ring. Empty rings are represented
+// as nil Ring pointers. The zero value for a Ring is a one-element
+// ring with a nil Value.
+//
+type Ring[T any] struct {
+	next, prev *Ring[T]
+	Value      T // for use by client; untouched by this library
+}
+
+func (r *Ring[T]) init() *Ring[T] {
+	r.next = r
+	r.prev = r
+	return r
+}
+
+// Next returns the next ring element. r must not be empty.
+func (r *Ring[T]) Next() *Ring[T] {
+	if r.next == nil {
+		return r.init()
+	}
+	return r.next
+}
+
+// Prev returns the previous ring element. r must not be empty.
+func (r *Ring[T]) Prev() *Ring[T] {
+	if r.next == nil {
+		return r.init()
+	}
+	return r.prev
+}
+
+// Move moves n % r.Len() elements backward (n < 0) or forward (n >= 0)
+// in the ring and returns that ring element. r must not be empty.
+//
+func (r *Ring[T]) Move(n int) *Ring[T] {
+	if r.next == nil {
+		return r.init()
+	}
+	switch {
+	case n < 0:
+		for ; n < 0; n++ {
+			r = r.prev
+		}
+	case n > 0:
+		for ; n > 0; n-- {
+			r = r.next
+		}
+	}
+	return r
+}
+
+// New creates a ring of n elements.
+func NewRing[T any](n int) *Ring[T] {
+	if n <= 0 {
+		return nil
+	}
+	r := new(Ring[T])
+	p := r
+	for i := 1; i < n; i++ {
+		p.next = &Ring[T]{prev: p}
+		p = p.next
+	}
+	p.next = r
+	r.prev = p
+	return r
+}
+
+// Link connects ring r with ring s such that r.Next()
+// becomes s and returns the original value for r.Next().
+// r must not be empty.
+//
+// If r and s point to the same ring, linking
+// them removes the elements between r and s from the ring.
+// The removed elements form a subring and the result is a
+// reference to that subring (if no elements were removed,
+// the result is still the original value for r.Next(),
+// and not nil).
+//
+// If r and s point to different rings, linking
+// them creates a single ring with the elements of s inserted
+// after r. The result points to the element following the
+// last element of s after insertion.
+//
+func (r *Ring[T]) Link(s *Ring[T]) *Ring[T] {
+	n := r.Next()
+	if s != nil {
+		p := s.Prev()
+		// Note: Cannot use multiple assignment because
+		// evaluation order of LHS is not specified.
+		r.next = s
+		s.prev = r
+		n.prev = p
+		p.next = n
+	}
+	return n
+}
+
+// Unlink removes n % r.Len() elements from the ring r, starting
+// at r.Next(). If n % r.Len() == 0, r remains unchanged.
+// The result is the removed subring. r must not be empty.
+//
+func (r *Ring[T]) Unlink(n int) *Ring[T] {
+	if n <= 0 {
+		return nil
+	}
+	return r.Link(r.Move(n + 1))
+}
+
+// Len computes the number of elements in ring r.
+// It executes in time proportional to the number of elements.
+//
+func (r *Ring[T]) Len() int {
+	n := 0
+	if r != nil {
+		n = 1
+		for p := r.Next(); p != r; p = p.next {
+			n++
+		}
+	}
+	return n
+}
+
+// Do calls function f on each element of the ring, in forward order.
+// The behavior of Do is undefined if f changes *r.
+func (r *Ring[T]) Do(f func(T)) {
+	if r != nil {
+		f(r.Value)
+		for p := r.Next(); p != r; p = p.next {
+			f(p.Value)
+		}
+	}
+}