php 生成器 yield

<?php

$start1 = memory_get_usage();
echo $start1.' bytes'.PHP_EOL;

$rangeNum = range(1, 100);
foreach ($rangeNum as $num) {
    echo $num . PHP_EOL;
}
$end =  memory_get_usage();
echo $end - $start1 .' bytes'.PHP_EOL;


function my_range($start, $limit) {
    for ($i=$start; $i<=$limit; $i++) {
        yield $i;
    }
}

$start2 = memory_get_usage();
echo $start2.' bytes'.PHP_EOL;

$rangeNum2 = my_range(1, 100);
foreach ($rangeNum2 as $num) {
    echo $num . PHP_EOL;
}
$end =  memory_get_usage();
echo $end - $start2 .' bytes'.PHP_EOL;