PHP生成器yield使用示例

<?php
function getLines($file) {
    $f = fopen($file, 'r');
    try {
        while ($line = fgets($f)) {
            yield $line;
        }
    } finally {
        fclose($f);
    }
}
 
foreach (getLines("sql.txt") as $n => $line) {
    echo $line; //逐行输出大文件
}
 
/*-----------------------------------------------------------------------*/
function xrange($start, $end, $step = 1) {
    for ($i = $start; $i <= $end; $i += $step) {
        yield $i;
    }
}  
 
foreach (xrange(1, 1000) as $num) {
    echo $num, "\n";  //生成大数组
} 
 
/*-----------------------------------------------------------------------*/
function get(){
    $sql = "select * from `user` limit 0,500000000";
    $stat = $pdo->query($sql);
    while ($row = $stat->fetch()) {
        yield $row;//逐行读出数据库行
    }
}
 
foreach (get() as $row) {
    var_dump($row);
} 
 
/*-----------------------------------------------------------------------------*/
function middleware($handlers,$arguments = []){
    //函数栈
    $stack = [];
    $result = null;
 
    foreach ($handlers as $handler) {
        // 每次循环之前重置，只能保存最后一个处理程序的返回值
        $result = null;
        $generator = call_user_func_array($handler, $arguments);
 
        if ($generator instanceof \Generator) {
            //将协程函数入栈,为重入做准备
            $stack[] = $generator;
 
            //获取协程返回参数
            $yieldValue = $generator->current();
 
            //检查是否重入函数栈
            if ($yieldValue === false) {
                break;
            }
        } elseif ($generator !== null) {
            //重入协程参数
            $result = $generator;
        }
    }
 
    $return = ($result !== null);
    //将协程函数出栈
    while ($generator = array_pop($stack)) {
        if ($return) {
            $generator->send($result);
        } else {
            $generator->next();
        }
    }
}
$abc = function(){
    echo "this is abc start \n";
    yield;
    echo "this is abc end \n";
};
 
$qwe = function (){
    echo "this is qwe start \n";
    $a = yield;
    echo $a."\n";
    echo "this is qwe end \n";
};
$one = function (){
    return 1;
};
 
middleware([$abc,$qwe,$one]);