Extract non-core functionality from go-cid into go-cidutil.

set.go

@@ -1,9 +1,5 @@
 package cid
 
-import (
-	"context"
-)
-
 // Set is a implementation of a set of Cids, that is, a structure
 // to which holds a single copy of every Cids that is added to it.
 type Set struct {
@@ -70,33 +66,3 @@ func (s *Set) ForEach(f func(c *Cid) error) error {
 	return nil
 }
 
-// StreamingSet is an extension of Set which allows to implement back-pressure
-// for the Visit function
-type StreamingSet struct {
-	Set *Set
-	New chan *Cid
-}
-
-// NewStreamingSet initializes and returns new Set.
-func NewStreamingSet() *StreamingSet {
-	return &StreamingSet{
-		Set: NewSet(),
-		New: make(chan *Cid),
-	}
-}
-
-// Visitor creates new visitor which adds a Cids to the set and emits them to
-// the set.New channel
-func (s *StreamingSet) Visitor(ctx context.Context) func(c *Cid) bool {
-	return func(c *Cid) bool {
-		if s.Set.Visit(c) {
-			select {
-			case s.New <- c:
-			case <-ctx.Done():
-			}
-			return true
-		}
-
-		return false
-	}
-}