项目中生成器应用，解决量级数据导出excel内存溢出

应用场景：全量数据导出excel

$list = function () use ($result, $areaList, $industryList, $channelList, $useStatusList, $billServiceFollow, $serviceOrderAmount, $statistics, $adminUserInfo, $implementerInfo, $salesInfo) {
            foreach ($result as $value) {
                $value['province_name'] = $areaList[$value['province_id']] ?? '无';//省份
                $value['city_name'] = $areaList[$value['city_id']] ?? '无';//城市

                $industry = $value['industry'] ?? 0;
                $value['industry_name'] = $industryList[$industry] ?? '无';//行业

                $channel = $value['channel'] ?? 0;
                $value['channel_name'] = $channelList[$channel] ?? '无';//客户来源

                $useStatus = $value['use_status'];
                $value['contract_type'] = $useStatusList[$useStatus] ?? '';//合同类型

                if ($useStatus == 1) {//正式合同
                    $startTime = $value['formal_starttime'] ?? 0;
                    if ($startTime == '0000-00-00 00:00:00') {
                        $startTime = 0;
                    }
                    $endTime = $value['formal_endtime'] ?? 0;
                    if ($startTime == '0000-00-00 00:00:00') {
                        $endTime = 0;
                    }
                    $value['contract_begin_date'] = !empty($startTime) ? date('Y-m-d', strtotime($startTime)) : '无';
                    $value['contract_end_date'] = !empty($endTime) ? date('Y-m-d', strtotime($endTime)) : '无';
                } else {//试用合同

                    $startTime = $value['tryout_starttime'] ?? 0;
                    if ($startTime == '0000-00-00 00:00:00') {
                        $startTime = 0;
                    }
                    $endTime = $value['tryout_endtime'] ?? 0;
                    if ($startTime == '0000-00-00 00:00:00') {
                        $endTime = 0;
                    }
                    $value['contract_begin_date'] = !empty($startTime) ? date('Y-m-d', strtotime($startTime)) : '无';
                    $value['contract_end_date'] = !empty($endTime) ? date('Y-m-d', strtotime($endTime)) : '无';
                }

                $value['acenum'] = $statistics[$value['id']]['acenum'] ?? 0;//账套数量
                $value['usernum'] = $statistics[$value['id']]['usernum'] ?? 0;//会计数量
                $value['vounum'] = $statistics[$value['id']]['vounum'] ?? 0;//凭证
                $value['billnum'] = $statistics[$value['id']]['billnum'] ?? 0;//上传票据

                //购买票据数量
                $totalServiceNum = $billServiceFollow[$value['id']]['total_service_num'] ?? 0;
                if ($totalServiceNum >= 100000000) {
                    $totalServiceNum = '不限量';
                }
                $value['total_service_num'] = $totalServiceNum;

                //成交金额
                $value['total_recive_amount'] = $serviceOrderAmount[$value['id']]['total_recive_amount'] ?? 0;
                $value['create_by_name'] = $adminUserInfo[$value['create_by']] ?? '无';

                //实施名称
                $implementer = $value['implement'] ?? 0;
                $value['implementer'] = $implementerInfo[$implementer] ?? '无';

                //销售
                $sale = $value['sale_id'] ?? 0;
                $value['sale'] = $salesInfo[$sale] ?? '无';

                $abutment = $value['abutment'] ?? 0;
                $value['abutment'] = $salesInfo[$abutment] ?? '无';
                yield $value;
            }
        };

        $data = [
            'list' => $list(),
        ];

        //调用下载excel
        $excel = new DownloadExcel();
        return $excel->title('客户列表')->subtitle('')->subject('')->fill('company-list', $data)->download();

解决问题：
内存溢出

知识点说明：
1.将大结果集的数据单元yield，传给生成器。
2.通过function()use{};匿名函数接收生成器作为结果。

$data = [
      'list' => $list(),
];

后续只需要迭代$data['list']即可。