php using aliases and imports

Allowing external fully qualified names to be referenced or imported through aliases is an important feature of namespaces. This is somewhat similar to how you can create symbolic links to other files or directories in a Unix-like file system.

PHP namespace supports two ways of using aliases or imports: using aliases for class names, or using aliases for namespace names. Note that PHP does not support imported functions or constants.

In PHP, aliases are implemented through the operator use. Here is an example using all three possible ways of importing:

Example #1 Use the use operator to import/use aliases

<?php
    namespace foo;
    use My\Full\Classname as Another;
    // 下面的例子与 use My\Full\NSname as NSname 相同
    use My\Full\NSname;
    // 导入一个全局类
    use \ArrayObject;
    $obj = new namespace\Another; // 实例化 foo\Another 对象
    $obj = new Another; // 实例化 My\Full\Classname　对象
    NSname\subns\func(); // 调用函数 My\Full\NSname\subns\func
    $a = new ArrayObject(array(1)); // 实例化 ArrayObject 对象
    // 如果不使用 "use \ArrayObject" ，则实例化一个 foo\ArrayObject 对象
?>

Be careful with names in namespaces (fully qualified names including namespace separators such as FooBar and For global names that do not contain namespace separators (such as FooBar), the leading backslash is unnecessary and not allowed, because the imported name must be fully qualified and will not be based on the current naming. Relative analysis of space.

In order to simplify the operation, PHP also supports multiple use statements in one line

Example #2 Import/use aliases through the use operator, multiple use statements are included in one line

<?php
    use My\Full\Classname as Another, My\Full\NSname;
    $obj = new Another; // 实例化 My\Full\Classname 对象
    NSname\subns\func(); // 调用函数 My\Full\NSname\subns\func
?>

The import operation is executed during compilation, but Dynamic class names, function names, or constant names are not.

Example #3 Import and dynamic names

<?php
    use My\Full\Classname as Another, My\Full\NSname;
    $obj = new Another; // 实例化一个 My\Full\Classname 对象
    $a = &#39;Another&#39;;
    $obj = new $a; // 实际化一个 Another 对象
?>

Also, the import operation only affects unqualified and qualified names. Fully qualified names are not affected by imports because they are deterministic.

Example #4 Import and fully qualified name

<?php
    use My\Full\Classname as Another, My\Full\NSname;
    $obj = new Another; // 实例化My\Full\Classname类的对象 
    $obj = new \Another; // 实例化Another类的对象 
    $obj = new Another\thing; // 实例化My\Full\Classname\thing类的对象 
    $obj = new \Another\thing; // 实例化Another\thing类的对象 
?>