PHP generator explanation and simple usage

1. Official description: Generators provide an easier way to implement simple object iteration. Compared with defining a class to implement the Iterator interface, the performance overhead and complexity are greatly reduced. Generators allow you to write code in a foreach block to iterate over a set of data without creating an array in memory.

2. The generator is just like an ordinary custom function. Unlike ordinary functions that only return once, the generator can yield as many times as needed to generate values ​​that need to be iterated.

3. Code example:

//未使用生成器
echo &#39;开始内存：&#39;.getMemory().&#39;<br>&#39;;
$nums = range(0,1000000);
echo &#39;结束内存：&#39;.getMemory().&#39;<br>&#39;;
//输出结果
//开始内存：0.23M
//结束内存：130.31

//使用生成器
echo &#39;开始内存：&#39;.getMemory().&#39;<br>&#39;;
$nums = xrange(1000000);
function xrange($total)
{
    for ($i = 0; $i < $total; $i++) {
        yield $i;
    }
}
echo &#39;结束内存：&#39;.getMemory().&#39;<br>&#39;;
//输出结果
//开始内存：0.23M
//结束内存：0.23M

4. Practical application example

/**
 * 大量数据生成示例
 * @param int $page
 * @param int $limit
 * @return Generator
 */
public function generator($page = 1,$limit = 50000)
{
    while (true) {
        echo "第{$page}次".&#39;generator开始内存：&#39;.$this->getMemory().&#39;<br>&#39;;
        $start = ($page-1) * $limit;
        $sql = "SELECT p.id,p.wh_code,p.goods_sn FROM p_product as p WHERE p.wh_code  LIKE &#39;%YB%&#39; OR p.wh_code  
        LIKE &#39;%DZWH%&#39; LIMIT {$start},{$limit} ";
        $resultAll = db()->fetchAll($sql);
        yield $resultAll; //生成器
        if (count($resultAll) != $limit) {
            break;
        }
        echo "第{$page}次".&#39;generator结束内存：&#39;.$this->getMemory().&#39;<br>&#39;;
        $page++;
    }
}
        //测试生成器内存消耗
//        foreach ($this->generator() as $result) {
//            var_dump($result[0]);
//        }

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