selectn blog snippets

select4.go

func select4(ctx context.Context, chanz []chan interface{}, res chan *r, r *r, i int) {
	select {
	case r.v, r.ok = <-chanz[0]:
		r.i = i + 0
		res <- r
	case r.v, r.ok = <-chanz[1]:
		r.i = i + 1
		res <- r
	case r.v, r.ok = <-chanz[2]:
		r.i = i + 2
		res <- r
	case r.v, r.ok = <-chanz[3]:
		r.i = i + 3
		res <- r
	case <-ctx.Done():
		break
	}
}

select8.go

func select8(ctx context.Context, chanz []chan interface{}, res chan *r, r *r, i int) {
	select {
	case r.v, r.ok = <-chanz[0]:
		r.i = i + 0
		res <- r
	case r.v, r.ok = <-chanz[1]:
		r.i = i + 1
		res <- r
	case r.v, r.ok = <-chanz[2]:
		r.i = i + 2
		res <- r
	case r.v, r.ok = <-chanz[3]:
		r.i = i + 3
		res <- r
	case r.v, r.ok = <-chanz[4]:
		r.i = i + 4
		res <- r
	case r.v, r.ok = <-chanz[5]:
		r.i = i + 5
		res <- r
	case r.v, r.ok = <-chanz[6]:
		r.i = i + 6
		res <- r
	case r.v, r.ok = <-chanz[7]:
		r.i = i + 7
		res <- r
	case <-ctx.Done():
		break
	}
}

selectn.go

	agg := aggPool.Get().(chan *r)
	defer aggPool.Put(agg)

	for i < len(channels) {
		l = len(channels) - i
		switch {
		case l > 31 && maxBachSize >= 32:
			go select32(ctx, channels[i:i+32], agg, rPool.Get().(*r), i)
			i += 32
		case l > 15 && maxBachSize >= 16:
			go select16(ctx, channels[i:i+16], agg, rPool.Get().(*r), i)
			i += 16
		case l > 7 && maxBachSize >= 8:
			go select8(ctx, channels[i:i+8], agg, rPool.Get().(*r), i)
			i += 8
		case l > 3 && maxBachSize >= 4:
			go select4(ctx, channels[i:i+4], agg, rPool.Get().(*r), i)
			i += 4
		case l > 1 && maxBachSize >= 2:
			go select2(ctx, channels[i:i+2], agg, rPool.Get().(*r), i)
			i += 2
		case l > 0:
			go select1(ctx, channels[i], agg, rPool.Get().(*r), i)
			i += 1
		}
	}

what if the len(channel) is dynamic?