# ArrayAccess（数组式访问）接口

(PHP 5, PHP 7, PHP 8)

## 简介

提供像访问数组一样访问对象的能力的接口。

## 接口摘要

interface ArrayAccess {
/* 方法 */
public function offsetExists(mixed `$offset`): bool
public function offsetGet(mixed `$offset`): mixed
public function offsetSet(mixed `$offset`, mixed `$value`): void
public function offsetUnset(mixed `$offset`): void
}

## 示例

示例 #1 基础用法

    <?php
    class Obj implements ArrayAccess {
        public $container = [
            "one"   => 1,
            "two"   => 2,
            "three" => 3,
        ];

        public function offsetSet($offset, $value): void {
            if (is_null($offset)) {
                $this->container[] = $value;
            } else {
                $this->container[$offset] = $value;
            }
        }

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

        public function offsetUnset($offset): void {
            unset($this->container[$offset]);
        }

        public function offsetGet($offset): mixed {
            return isset($this->container[$offset]) ? $this->container[$offset] : null;
        }
    }

    $obj = new Obj;

    var_dump(isset($obj["two"]));
    var_dump($obj["two"]);
    unset($obj["two"]);
    var_dump(isset($obj["two"]));
    $obj["two"] = "A value";
    var_dump($obj["two"]);
    $obj[] = 'Append 1';
    $obj[] = 'Append 2';
    $obj[] = 'Append 3';
    print_r($obj);
    ?>

以上示例的输出类似于：

    bool(true)
    int(2)
    bool(false)
    string(7) "A value"
    obj Object
    (
        [container:obj:private] => Array
            (
                [one] => 1
                [three] => 3
                [two] => A value
                [0] => Append 1
                [1] => Append 2
                [2] => Append 3
            )

    )

## 目录

- ArrayAccess::offsetExists — 检查一个偏移位置是否存在
- ArrayAccess::offsetGet — 获取一个偏移位置的值
- ArrayAccess::offsetSet — 设置一个偏移位置的值
- ArrayAccess::offsetUnset — 复位一个偏移位置的值

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