php数组怪事，求解答
php
class dd {
const d = 'd';
public function test() {
$arr = array();
$arr['d'] = 'test';
$arr2 = array(
'a' => '1',
'b' => '2',
'c' => '3',
'd' => '4'
);
foreach ($arr2 as $key=>$value) {
if (in_array($key,array('a','b','c')) || isset($arr['self::d'])) {
echo $key;
}
}
}
}
$dd = new dd();
$dd->test();
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输出：
<code>abc </code>
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为什么不是输出abcd
========补充一下======== 其实我真正想问的是，单引号不是不解析么？为什么echo $arr['self::d']。提示的是未定义'self::d'这个常量？提示是为定义'self::d'可不是'd'哦。
=======我是分割线========
