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;
}
}
希望本文所述对大家PHP程序设计有所帮助。
