fast remove item from slice

removeSlice.go

func clearExpiredTx(txs types.Transactions, now time.Time) types.Transactions {
	for i := 0; i < len(txs); i++ {
		if !txs[i].Expired(now) {
			continue
		}
		if len(txs) == 1 {
			return nil
		}
		var last *types.Transaction
		for {
			last = txs[len(txs)-1]
			if !last.Expired(now) {
				break
			}
			//remove last
			txs[len(txs)-1] = nil
			txs = txs[:len(txs)-1]
			last = nil
			if len(txs) == 0 {
				break
			}
		}
		if last == nil || len(txs)-1 < i {
			return txs
		}
		txs[i] = last
		txs[len(txs)-1] = nil
		txs = txs[:len(txs)-1]
	}
	return txs
}