PHP預(yù)定義接口：ArrayAccess

簡(jiǎn)介

• 提供像訪問(wèn)數(shù)組一樣訪問(wèn)對(duì)象的能力的接口。

接口摘要

ArrayAccess {
/* 方法 */
abstract public boolean offsetExists ( mixed $offset )
abstract public mixed offsetGet ( mixed $offset )
abstract public void offsetSet ( mixed $offset , mixed $value )
abstract public void offsetUnset ( mixed $offset )
}

目錄

• ArrayAccess::offsetExists — 檢查一個(gè)偏移位置是否存在
• ArrayAccess::offsetGet — 獲取一個(gè)偏移位置的值
• ArrayAccess::offsetSet — 設(shè)置一個(gè)偏移位置的值
• ArrayAccess::offsetUnset — 復(fù)位一個(gè)偏移位置的值

代碼演示

class Obj implements ArrayAccess
{
    private $container = [];

    public function offsetExists($offset): bool
    {
        echo '調(diào)用' . __METHOD__ . '方法' . PHP_EOL;
        echo print_r(func_get_args(), true);

        return isset($this->container[$offset]);
    }

    public function offsetGet($offset)
    {
        echo '調(diào)用' . __METHOD__ . '方法' . PHP_EOL;
        echo print_r(func_get_args(), true);

        return $this->container[$offset] ?? null;
    }

    public function offsetSet($offset, $value)
    {
        echo '調(diào)用' . __METHOD__ . '方法' . PHP_EOL;
        echo print_r(func_get_args(), true);
        $this->container[$offset] = $value;
    }

    public function offsetUnset($offset)
    {
        echo '調(diào)用' . __METHOD__ . '方法' . PHP_EOL;
        echo print_r(func_get_args(), true);

        unset($this->container[$offset]);
    }
}

//實(shí)例化對(duì)象
$zhangsan = new Obj();

//賦值
$zhangsan['name'] = '張三';//調(diào)用Obj::offsetSet方法

//輸出
echo $zhangsan['name'] . PHP_EOL;//調(diào)用Obj::offsetGet方法

//校驗(yàn)是否存在
isset($zhangsan['name']) . PHP_EOL;//調(diào)用Obj::offsetExists方法

//刪除數(shù)組單元
unset($zhangsan['name']);//調(diào)用Obj::offsetUnset方法

逆向思考：

通過(guò)調(diào)用接口方法來(lái)實(shí)現(xiàn)對(duì)對(duì)象屬性進(jìn)行操作，然后使用數(shù)組的方式訪問(wèn)

$zhangsan=new Obj();

if ($zhangsan instanceof \ArrayAccess) {
    //通過(guò)調(diào)用接口方法為對(duì)象賦值
    $zhangsan->offsetSet('name', '張三');

    //通過(guò)數(shù)組方式取值
    echo $zhangsan['name'] . PHP_EOL;
    //通過(guò)調(diào)用接口方法取值
    echo $zhangsan->offsetGet('name').PHP_EOL;

    //通過(guò)調(diào)用接口方法來(lái)判斷對(duì)象屬性是否存在
    if (!$zhangsan->offsetExists('age') && !isset($zhangsan['age'])) {
        $zhangsan->offsetSet('age', '18');
    }

    $zhangsan['address']='北京';
    //通過(guò)調(diào)用接口方法來(lái)判斷對(duì)象屬性
    $zhangsan->offsetUnset('address');

    echo $zhangsan['address'] ?? 'address is not exists';

    //直接為對(duì)象屬性賦值（不可行）
    $zhangsan->school='Peking University';
    echo $zhangsan['school'] ?? 'school is not exists';//school is not exists
}

應(yīng)用案例演示

實(shí)現(xiàn)配置文件信息讀取

準(zhǔn)備工作:

按照一下給出的目錄結(jié)構(gòu)建立文件

./
├── config
│?? ├── app.php
│?? └── database.php
└── config.php

• ./config/app.php

  <?php
  return [
      'name' => 'app name',
      'version' => 'v1.0.0'
  ];

• ./config/database.php

  <?php
  return [
      'mysql' => [
          'host' => 'localhost',
          'user' => 'root',
          'password' => '12345678'
      ]
  ];

• ./config.php

<?php

namespace Config;

final Class Config implements \ArrayAccess
{
    private $config = [];
    private static $instance = null;
    private $path = null;

    private function __construct()
    {
        $this->path = __DIR__ . '/config/';
    }

    //單例模式獲取實(shí)例
    public static function getInstance()
    {
        if (!self::$instance instanceof self) {
            self::$instance = new self;
        }
        return self::$instance;
    }

    //防止被克隆
    private function __clone()
    {
    }

    public function offsetExists($offset)
    {
        return isset($this->config[$offset]);
    }

    public function offsetGet($offset)
    {
        if (!isset($this->config[$offset]) || empty($this->config[$offset])) {
            //裝載配置文件
            $this->config[$offset] = require $this->path . $offset . '.php';
        }
        return $this->config[$offset];
    }

    public function offsetSet($offset, $value)
    {
        throw new \Exception('不提供設(shè)置配置');
    }

    public function offsetUnset($offset)
    {
        throw new \Exception('不提供刪除配置');
    }
}

$config = Config::getInstance();

//獲取app.php 文件的 name
echo $config['app']['name'].PHP_EOL; //app name

//獲取database.php文件mysql的user配置
echo $config['database']['mysql']['user'].PHP_EOL; // root