php namespace error

<code>
<?php

namespace Article;
const PATH = '/article';
function getCommentTotal() {
    return 100;
}
class Comment { }

namespace MessageBoard;
const PATH = '/message_board';
function getCommentTotal() {
    return 300;
}
class Comment { }

//调用当前空间的常量、函数和类
echo PATH; ///message_board
echo getCommentTotal(); //300
$comment = new Comment();

//调用Article空间的常量、函数和类
echo \Article\PATH; ///article
echo \Article\getCommentTotal(); //100
$article_comment = new \Article\Comment();
?>
</code>

<code>
<?php

namespace Article;
const PATH = '/article';
function getCommentTotal() {
    return 100;
}
class Comment { }

namespace MessageBoard;
const PATH = '/message_board';
function getCommentTotal() {
    return 300;
}
class Comment { }

//调用当前空间的常量、函数和类
echo PATH; ///message_board
echo getCommentTotal(); //300
$comment = new Comment();

//调用Article空间的常量、函数和类
echo \Article\PATH; ///article
echo \Article\getCommentTotal(); //100
$article_comment = new \Article\Comment();
?>
</code>