PHP5.5新特性之yield理解与用法实例分析

本文实例讲述了PHP5.5新特性之yield理解与用法。分享给大家供大家参考，具体如下：yield生

本文实例讲述了PHP5.5新特性之yield理解与用法。分享给大家供大家参考，具体如下：

yield生成器是php5.5之后出现的，yield提供了一种更容易的方法来实现简单的迭代对象，相比较定义类实现 Iterator 接口的方式，性能开销和复杂性大大降低。

yield生成器允许你 在 foreach 代码块中写代码来迭代一组数据而不需要在内存中创建一个数组。

使用示例：

/**
 * 计算平方数列
 * @param $start
 * @param $stop
 * @return Generator
 */
function squares($start, $stop) {
 if ($start < $stop) {
 for ($i = $start; $i <= $stop; $i++) {
 yield $i => $i * $i;
 }
 }
 else {
 for ($i = $start; $i >= $stop; $i--) {
 yield $i => $i * $i; //迭代生成数组： 键=》值
 }
 }
}
foreach (squares(3, 15) as $n => $square) {
 echo $n . 'squared is' . $square . '<br>';
}

输出：

    3 squared is 9     4 squared is 16     5 squared is 25     ...

示例2：

//对某一数组进行加权处理
$numbers = array('nike' => 200, 'jordan' => 500, 'adiads' => 800);
//通常方法，如果是百万级别的访问量，这种方法会占用极大内存
function rand_weight($numbers)
{
 $total = 0;
 foreach ($numbers as $number => $weight) {
 $total += $weight;
 $distribution[$number] = $total;
 }
 $rand = mt_rand(0, $total-1);
 foreach ($distribution as $num => $weight) {
 if ($rand < $weight) return $num;
 }
}
//改用yield生成器
function mt_rand_weight($numbers) {
 $total = 0;
 foreach ($numbers as $number => $weight) {
 $total += $weight;
 yield $number => $total;
 }
}
function mt_rand_generator($numbers)
{
 $total = array_sum($numbers);
 $rand = mt_rand(0, $total -1);
 foreach (mt_rand_weight($numbers) as $num => $weight) {
 if ($rand < $weight) return $num;
 }
}