<?php
function gen_one_to_three() {
  for ($i = 1; $i <= 3; $i++) {
    //注意變量$i的值在不同的yield之間是保持傳遞的。
    yield $i;
  }
}
$generator = gen_one_to_three();
foreach ($generator as $value) {
  echo "$value\n";
}
?>

/**
 * 計算平方數(shù)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(shù)組： 鍵=》值
    }
  }
}
foreach (squares(3, 15) as $n => $square) {
  echo $n . ‘squared is‘ . $square . ‘<br>‘;
}

//對某一數(shù)組進行加權處理
$numbers = array(‘nike‘ => 200, ‘jordan‘ => 500, ‘a(chǎn)diads‘ => 800);
//通常方法，如果是百萬級別的訪問量，這種方法會占用極大內存
function rand_weight($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;
  }
}