本文實例講述了PHP5.5新特性之yield理解與用法。分享給大家供大家參考，具體如下：
yield生成器是php5.5之后出現的，yield提供了一種更容易的方法來實現簡單的迭代對象，相比較定義類實現 Iterator 接口的方式，性能開銷和復雜性大大降低。
yield生成器允許你 在 foreach 代碼塊中寫代碼來迭代一組數據而不需要在內存中創(chuàng)建一個數組。
使用示例：
/**
* 計算平方數列
* @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; //迭代生成數組： 鍵=》值
}
}
}
foreach (squares(3, 15) as $n => $square) {
echo $n . 'squared is' . $square . '<br>';
}
輸出：
3 squared is 9
4 squared is 16
5 squared is 25
...
示例2：
//對某一數組進行加權處理
$numbers = array('nike' => 200, 'jordan' => 500, 'adiads' => 800);
//通常方法，如果是百萬級別的訪問量，這種方法會占用極大內存
function rand_weight($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;
}
}
希望本文所述對大家PHP程序設計有所幫助。
