Using namespaces: Aliasing/Importing
(PHP 5 >= 5.3.0, PHP 7)
The ability to refer to an external fully qualified name with an alias, or importing, is an important feature of namespaces. This is similar to the ability of unix-based filesystems to create symbolic links to a file or to a directory.
All versions of PHP that support namespaces support three kinds of aliasing or importing: aliasing a class name, aliasing an interface name, and aliasing a namespace name. PHP 5.6+ also allows aliasing or importing function and constant names.
In PHP, aliasing is accomplished with the use operator. Here is an example showing all 5 kinds of importing:
Example #1 importing/aliasing with the use operator
<?php
namespace?foo;
use?My\Full\Classname?as?Another;
//?this?is?the?same?as?use?My\Full\NSname?as?NSname
use?My\Full\NSname;
//?importing?a?global?class
use?ArrayObject;
//?importing?a?function?(PHP?5.6+)
use?function?My\Full\functionName;
//?aliasing?a?function?(PHP?5.6+)
use?function?My\Full\functionName?as?func;
//?importing?a?constant?(PHP?5.6+)
use?const?My\Full\CONSTANT;
$obj?=?new?namespace\Another;?//?instantiates?object?of?class?foo\Another
$obj?=?new?Another;?//?instantiates?object?of?class?My\Full\Classname
NSname\subns\func();?//?calls?function?My\Full\NSname\subns\func
$a?=?new?ArrayObject(array(1));?//?instantiates?object?of?class?ArrayObject
//?without?the?"use?ArrayObject"?we?would?instantiate?an?object?of?class?foo\ArrayObject
func();?//?calls?function?My\Full\functionName
echo?CONSTANT;?//?echoes?the?value?of?My\Full\CONSTANT
?>Note that for namespaced names (fully qualified namespace names containing namespace separator, such as Foo\Bar as opposed to global names that do not, such as FooBar), the leading backslash is unnecessary and not recommended, as import names must be fully qualified, and are not processed relative to the current namespace.
PHP additionally supports a convenience shortcut to place multiple use statements on the same line
Example #2 importing/aliasing with the use operator, multiple use statements combined
<?php
use?My\Full\Classname?as?Another,?My\Full\NSname;
$obj?=?new?Another;?//?instantiates?object?of?class?My\Full\Classname
NSname\subns\func();?//?calls?function?My\Full\NSname\subns\func
?>Importing is performed at compile-time, and so does not affect dynamic class, function or constant names.
Example #3 Importing and dynamic names
<?php
use?My\Full\Classname?as?Another,?My\Full\NSname;
$obj?=?new?Another;?//?instantiates?object?of?class?My\Full\Classname
$a?=?'Another';
$obj?=?new?$a;??????//?instantiates?object?of?class?Another
?>In addition, importing only affects unqualified and qualified names. Fully qualified names are absolute, and unaffected by imports.
Example #4 Importing and fully qualified names
<?php
use?My\Full\Classname?as?Another,?My\Full\NSname;
$obj?=?new?Another;?//?instantiates?object?of?class?My\Full\Classname
$obj?=?new?\Another;?//?instantiates?object?of?class?Another
$obj?=?new?Another\thing;?//?instantiates?object?of?class?My\Full\Classname\thing
$obj?=?new?\Another\thing;?//?instantiates?object?of?class?Another\thing
?>Scoping rules for importing
The use keyword must be declared in the outermost scope of a file (the global scope) or inside namespace declarations. This is because the importing is done at compile time and not runtime, so it cannot be block scoped. The following example will show an illegal use of the use keyword:
Example #5 Illegal importing rule
<?php
namespace?Languages;
function?toGreenlandic()
{
????use?Languages\Danish;
????//?...
}
?>Note: Importing rules are per file basis, meaning included files will NOT inherit the parent file's importing rules.
Group use declarations
From PHP 7.0 onwards, classes, functions and constants being imported from the same namespace can be grouped together in a single use statement.
<?php
//?Pre?PHP?7?code
use?some\namespace\ClassA;
use?some\namespace\ClassB;
use?some\namespace\ClassC?as?C;
use?function?some\namespace\fn_a;
use?function?some\namespace\fn_b;
use?function?some\namespace\fn_c;
use?const?some\namespace\ConstA;
use?const?some\namespace\ConstB;
use?const?some\namespace\ConstC;
//?PHP?7+?code
use?some\namespace\{ClassA,?ClassB,?ClassC?as?C};
use?function?some\namespace\{fn_a,?fn_b,?fn_c};
use?const?some\namespace\{ConstA,?ConstB,?ConstC};← namespace keyword and __NAMESPACE__ constant
? 1997–2017 The PHP Documentation GroupLicensed under the Creative Commons Attribution License v3.0 or later.
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