Golang Iterator.UID方法代碼示例

// optimizeOrder(l) takes a list and returns a list, containing the same contents
// but with a new ordering, however it wishes.
func (it *And) optimizeOrder(its []graph.Iterator) []graph.Iterator {
	var (
		// bad contains iterators that can't be (efficiently) nexted, such as
		// graph.Optional or graph.Not. Separate them out and tack them on at the end.
		out, bad []graph.Iterator
		best     graph.Iterator
		bestCost = int64(1 << 62)
	)

	// Find the iterator with the projected "best" total cost.
	// Total cost is defined as The Next()ed iterator's cost to Next() out
	// all of it's contents, and to Contains() each of those against everyone
	// else.
	for _, root := range its {
		if _, canNext := root.(graph.Nexter); !canNext {
			bad = append(bad, root)
			continue
		}
		rootStats := root.Stats()
		cost := rootStats.NextCost
		for _, f := range its {
			if _, canNext := f.(graph.Nexter); !canNext {
				continue
			}
			if f == root {
				continue
			}
			stats := f.Stats()
			cost += stats.ContainsCost * (1 + (rootStats.Size / (stats.Size + 1)))
		}
		cost *= rootStats.Size
		if clog.V(3) {
			clog.Infof("And: %v Root: %v Total Cost: %v Best: %v", it.UID(), root.UID(), cost, bestCost)
		}
		if cost < bestCost {
			best = root
			bestCost = cost
		}
	}
	if clog.V(3) {
		clog.Infof("And: %v Choosing: %v Best: %v", it.UID(), best.UID(), bestCost)
	}

	// TODO(barakmich): Optimization of order need not stop here. Picking a smart
	// Contains() order based on probability of getting a false Contains() first is
	// useful (fail faster).

	// Put the best iterator (the one we wish to Next()) at the front...
	out = append(out, best)

	// ... push everyone else after...
	for _, it := range its {
		if _, canNext := it.(graph.Nexter); !canNext {
			continue
		}
		if it != best {
			out = append(out, it)
		}
	}

	// ...and finally, the difficult children on the end.
	return append(out, bad...)
}