<?php
 
class Klass implements Serializable {
  // 被演算子（シリアライズする）
  private $a;
  // 被演算子（シリアライズする）
  private $b;
 
  // 再計算が必要かどうかを表す（シリアライズしたくない）
  private $needCalc;
  // 計算結果（シリアライズしたくない）
  private $cache;
 
  public function __construct($a, $b) {
    $this->a = $a;
    $this->b = $b;
    $this->needCalc = true;
    $this->cache = null;
  }
 
  public function getResult() {
    if ($this->needCalc) {
      $this->cache = $this->calc();
      $this->needCalc = false;
    }
    return $this->cache;
  }
 
  private function calc() {
    return $this->a + $this->b;
  }
 
  public function serialize() {
    return serialize(array($this->a, $this->b));
  }
 
  public function unserialize($serialized) {
    $ar = unserialize($serialized);
    $this->a = $ar[0];
    $this->b = $ar[1];
    $this->needCalc = true;
    $this->cache = null;
  }
}
 
// インスタンス化およびキャッシング
$obj = new Klass(42, 23);
var_dump($obj);
$obj->getResult();
var_dump($obj);
 
// シリアライズ不要なフィールドは捨てられたか？
$ser = serialize($obj);
var_dump($ser);
 
// シリアライズしなかったフィールドに
// 正しく初期値が与えられているか？
$newObj = unserialize($ser);
var_dump($newObj);
$newObj->getResult();
var_dump($newObj);

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