命名空间和动态语言特征

PHP

PHP 命名空间的实现受到其语言自身的动态特征的影响。因此，如果要将下面的代码转换到命名空间中：

<?php
class classname
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function funcname()
{
    echo __FUNCTION__,"\n";
}
const constname = "global";
$a = 'classname';
$obj = new $a; // prints classname::__construct
$b = 'funcname';
$b(); // prints funcname
echo constant('constname'), "\n"; // prints global
?>

必须使用完全限定名称（包括命名空间前缀的类名称）。注意因为在动态的类名称、函数名称或常量名称中，限定名称和完全限定名称没有区别，因此其前导的反斜杠是不必要的。

<?php
namespace namespacename;
class classname
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function funcname()
{
    echo __FUNCTION__,"\n";
}
const constname = "namespaced";
include 'example1.php';
$a = 'classname';
$obj = new $a; // prints classname::__construct
$b = 'funcname';
$b(); // prints funcname
echo constant('constname'), "\n"; // prints global
/* note that if using double quotes, "\\namespacename\\classname" must be used */
$a = '\namespacename\classname';
$obj = new $a; // prints namespacename\classname::__construct
$a = 'namespacename\classname';
$obj = new $a; // also prints namespacename\classname::__construct
$b = 'namespacename\funcname';
$b(); // prints namespacename\funcname
$b = '\namespacename\funcname';
$b(); // also prints namespacename\funcname
echo constant('\namespacename\constname'), "\n"; // prints namespaced
echo constant('namespacename\constname'), "\n"; // also prints namespaced
?>

请一定别忘了阅读 对字符串中的命名空间名称转义的注解.

Dynamic namespace names (quoted identifiers) should escape backslash

• It is very important to realize that because the backslash is used as an escape character within strings, it should always be doubled when used inside a string. Otherwise there is a risk of unintended consequences:
• Example #9 Dangers of using namespaced names inside a double-quoted string

<?php
$a = new "dangerous\name"; // \n is a newline inside double quoted strings!
$obj = new $a;
$a = new 'not\at\all\dangerous'; // no problems here.
$obj = new $a;
?>

Inside a single-quoted string, the backslash escape sequence is much safer to use, but it is still recommended practice to escape backslashes in all strings as a best practice.

我的理解:

• ""和''的区别
• \最后写成\\转义字符