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    Namespaces verwenden: Aliase/Importieren

    (PHP 5 >= 5.3.0, PHP 7, PHP 8)

    Die Möglichkeit, auf vollständig qualifizierte Namen mit einem Alias (Importieren) zuzugreifen, ist ein wichtiges Feature von Namespaces. Dies ist ähnlich wie die Möglichkeit von Unix-basierten Dateisystemen einen symbolischen Link auf eine Datei oder ein Verzeichnis anzulegen.

    PHP unterstützt das Vergeben von Aliasen (Importe) für Konstanten, Funktionen, Klassen, Interfaces, Traits, Aufzählungen (Enums) und Namespaces.

    Ein Alias wird mittels des use-Operators angelegt. Hier ein Beispiel, welches alle fünf Arten von Importen zeigt:

    Beispiel #1 Aliase/Importieren mit dem use-Operator

    <?php
    namespace foo;
    use     My\Full\Classname as Another;

    // dies ist das gleiche wie use My\Full\NSname as NSname
    use My\Full\NSname;

    // importiert eine globale Klasse
    use ArrayObject;

    // Eine Funktion importieren
    use function My\Full\functionName;

    // Alias für eine Funktion
    use function My\Full\functionName as func;

    // Eine Konstante importieren
    use const My\Full\CONSTANT;

    $obj = new namespace\Another; // erzeugt ein Objekt der Klasse foo\Another
    $obj = new Another; // erzeugt ein Objekt der Klasse My\Full\Classname
    NSname\subns\func(); // ruft die Funktion My\Full\NSname\subns\func auf
    $a = new ArrayObject(array(1)); // erzeugt ein Objekt der Klasse ArrayObject
    // ohne das "use ArrayObject" wäre ein Objekt der Klasse foo\ArrayObject erzeugt worden
    func(); // ruft die Funktion My\Full\functionName auf
    echo CONSTANT; // Gibt den Wert von My\Full\CONSTANT aus
    ?>
    Beachten Sie, dass für Namen von Namespaces (vollständig qualifizierte Namespacenamen mit einem Namensraumseparator, wie Foo\Bar, im Gegensatz zu globalen Namen ohne Separator, wie FooBar) der führende Backslash nicht notwendig und nicht empfohlen ist, weil importierte Namen vollständig qualifiziert sein müssen und nicht relativ zum aktuellen Namespace verarbeitet werden.

    PHP unterstützt zusätzlich auch eine komfortable Kurzsyntax, mit der mehrere use-Ausdrücke in der gleichen Zeile erscheinen können.

    Beispiel #2 Aliase/Importieren mit dem use-Operator, mehrere use-Ausdrücke kombiniert

    <?php
    use My\Full\Classname as Another, My\Full\NSname;

    $obj = new Another; // erzeugt ein Objekt der Klasse My\Full\Classname
    NSname\subns\func(); // ruft die Funktion My\Full\NSname\subns\func auf
    ?>

    Importieren wird zur Kompilierungszeit ausgeführt und hat daher keinen Einfluss auf dynamische Klassen-, Funktions- oder Konstantennamen.

    Beispiel #3 Importieren und dynamische Namen

    <?php
    use My\Full\Classname as Another, My\Full\NSname;

    $obj = new Another; // erzeugt ein Objekt der Klasse My\Full\Classname
    $a = 'Another';
    $obj = new $a; // erzeugt ein Objekt der Klasse Another
    ?>

    Zusätzlich beeinflusst das Importieren nur unqualifizierte und qualifizierte Namen. Vollständig qualifizierte Namen sind absolut und werden von Importen nicht beeinflusst.

    Beispiel #4 Importieren und vollständig qualifizierte Namen

    <?php
    use My\Full\Classname as Another, My\Full\NSname;

    $obj = new Another; // erzeugt ein Objekt der Klasse My\Full\Classname
    $obj = new \Another; // erzeugt ein Objekt der Klasse Another
    $obj = new Another\thing; // erzeugt ein Objekt der Klasse My\Full\Classname\thing
    $obj = new \Another\thing; // erzeugt ein Objekt der Klasse Another\thing
    ?>

    Gültigkeitsbereiche für Importe

    Das Schlüsselwort use muss im äußersten Gültigkeitsbereich (dem globalen Gültigkeitsbereich) oder innerhalb einer Namespace-Deklaration angegeben werden. Das ist darin begründet, dass Importe zur Kompilierungszeit und nicht zur Laufzeit durchgeführt werden und daher nicht in einem anderen Gültigkeitsbereich liegen dürfen. Das folgende Beispiel zeigt eine ungültige Verwendung des use-Schlüsselwortes:

    Beispiel #5 Ungültige Importregel

    <?php
    namespace Languages;

    function     toGreenlandic()
    {
    use     Languages\Danish;

    // ...
    }
    ?>

    Hinweis:

    Importregeln sind auf Dateibasis gültig, das heißt eine eingebundene Datei wird NICHT die Importregeln der einbindenden Datei erben.

    Gruppierte use Deklarationen

    Klassen, Funktionen und Konstanten, die aus dem gleichen Namespace importiert werden, in einer einzigen use Anweisung gruppiert werden.

    <?php

    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;

    // gleichbedeutend zu folgender gruppierter Use-Deklaration
    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};
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    User Contributed Notes 21 notes

    up
    171
    dominic_mayers at yahoo dot com
    8 years ago
    The keyword "use" has been recycled for three distinct applications:
    1- to import/alias classes, traits, constants, etc. in namespaces,
    2- to insert traits in classes,
    3- to inherit variables in closures.
    This page is only about the first application: importing/aliasing. Traits can be inserted in classes, but this is different from importing a trait in a namespace, which cannot be done in a block scope, as pointed out in example 5. This can be confusing, especially since all searches for the keyword "use" are directed to the documentation here on importing/aliasing.
    up
    141
    anon
    10 years ago
    The <?php use ?> statement does not load the class file. You have to do this with the <?php require ?> statement or by using an autoload function.
    up
    48
    Mawia HL
    7 years ago
    Here is a handy way of importing classes, functions and conts using a single use keyword:

    <?php
    use Mizo\Web\ {
           Php\WebSite,
           Php\KeyWord,
           Php\UnicodePrint,
           JS\JavaScript,
       function     JS\printTotal,
       function     JS\printList,
       const     JS\BUAIKUM,
       const     JS\MAUTAM
    };
    ?>
    up
    77
    k at webnfo dot com
    11 years ago
    Note that you can not alias global namespace:

    use \ as test;

    echo test\strlen('');

    won't work.
    up
    29
    xzero at elite7hackers dot net
    7 years ago
    I couldn't find answer to this question so I tested myself.
    I think it's worth noting:

    <?php
    use ExistingNamespace\NonExsistingClass;
    use     ExistingNamespace\NonExsistingClass as whatever;
    use     NonExistingNamespace\NonExsistingClass;
    use     NonExistingNamespace\NonExsistingClass as whatever;
    ?>

    None of above will actually cause errors unless you actually try to use class you tried to import.

    <?php
    // And this code will issue standard PHP error for non existing class.
    use ExistingNamespace\NonExsistingClass as whatever;
    $whatever = new whatever();
    ?>
    up
    17
    me at ruslanbes dot com
    8 years ago
    Note the code `use ns1\c1` may refer to importing class `c1` from namespace `ns1` as well as importing whole namespace `ns1\c1` or even import both of them in one line. Example:

    <?php
    namespace ns1;

    class     c1{}

    namespace     ns1\c1;

    class     c11{}

    namespace     main;

    use     ns1\c1;

    $c1 = new c1();
    $c11 = new c1\c11();

    var_dump($c1); // object(ns1\c1)#1 (0) { }
    var_dump($c11); // object(ns1\c1\c11)#2 (0) { }
    up
    29
    c dot 1 at smithies dot org
    13 years ago
    If you are testing your code at the CLI, note that namespace aliases do not work!

    (Before I go on, all the backslashes in this example are changed to percent signs because I cannot get sensible results to display in the posting preview otherwise. Please mentally translate all percent signs henceforth as backslashes.)

    Suppose you have a class you want to test in myclass.php:

    <?php
    namespace my%space;
    class     myclass {
    // ...
    }
    ?>

    and you then go into the CLI to test it. You would like to think that this would work, as you type it line by line:

    require 'myclass.php';
    use my%space%myclass; // should set 'myclass' as alias for 'my%space%myclass'
    $x = new myclass; // FATAL ERROR

    I believe that this is because aliases are only resolved at compile time, whereas the CLI simply evaluates statements; so use statements are ineffective in the CLI.

    If you put your test code into test.php:
    <?php
    require 'myclass.php';
    use     my%space%myclass;
    $x = new myclass;
    //...
    ?>
    it will work fine.

    I hope this reduces the number of prematurely bald people.
    up
    18
    cl
    11 years ago
    Something that is not immediately obvious, particular with PHP 5.3, is that namespace resolutions within an import are not resolved recursively.  i.e.: if you alias an import and then use that alias in another import then this latter import will not be fully resolved with the former import.

    For example:
    use \Controllers as C;
    use C\First;
    use C\Last;

    Both the First and Last namespaces are NOT resolved as \Controllers\First or \Controllers\Last as one might intend.
    up
    19
    x at d dot a dot r dot k dot REMOVEDOTSANDTHIS dot gray dot org
    11 years ago
    You are allowed to "use" the same resource multiple times as long as it is imported under a different alias at each invocation.

    For example:

    <?php
    use Lend;
    use     Lend\l1;
    use     Lend\l1 as l3;
    use     Lend\l2;
    use     Lend\l1\Keller;
    use     Lend\l1\Keller as Stellar;
    use     Lend\l1\Keller as Zellar;
    use     Lend\l2\Keller as Dellar;

    ...

    ?>

    In the above example, "Keller", "Stellar", and "Zellar" are all references to "\Lend\l1\Keller", as are "Lend\l1\Keller", "l1\Keller", and "l3\Keller".
    up
    1
    eithed at google mail
    3 years ago
    Bear in mind that it's perfectly fine to alias namespaces, ie:

    <?php
    use A\B\C\D\E\User;

    new     User();
    ?>

    can be also written as:

    <?php
    use A\B\C\D\E as ENamespace;

    new     ENamespace\User();
    ?>

    however following will not work:

    <?php
    use A\B\C\D\E as ENamespace;
    use     ENamespace\User;

    new     User();
    ?>

    > PHP Error:  Class "ENamespace\User" not found
    up
    3
    ultimater at gmail dot com
    8 years ago
    Note that "use" importing/aliasing only applies to the current namespace block.

    <?php

    namespace SuperCoolLibrary
    {
        class     Meta
            {
            static public function     getVersion()
            {
                return     '2.7.1';
            }
        }
    }

    namespace
    {
        use     SuperCoolLibrary\Meta;
        echo     Meta::getVersion();//outputs 2.7.1
    }

    namespace
    {
        echo     Meta::getVersion();//fatal error
    }

    ?>

    To get the expected behavior, you'd use:
    class_alias('SuperCoolLibrary\Meta','Meta');
    up
    2
    ZhangLiang
    7 years ago
    In Chinese,there is an error in translation:
    // 如果不使用 "use \ArrayObject" ，则实例化一个 foo\ArrayObject 对象
    it should be
    // 如果不使用 "use ArrayObject" ，则实例化一个 foo\ArrayObject 对象

    /*********************************************/
    中文下翻译有错误
    // 如果不使用 "use \ArrayObject" ，则实例化一个 foo\ArrayObject 对象
    这句话应该是
    // 如果不使用 "use ArrayObject" ，则实例化一个 foo\ArrayObject 对象
    up
    0
    tuxedobob
    2 years ago
    Note that because this is processed at compile time, this doesn't work when running PHP in interactive mode. use commands won't throw an error, but they won't do anything, either.
    up
    0
    thinice at gmail.com
    14 years ago
    Because imports happen at compile time, there's no polymorphism potential by embedding the use keyword in a conditonal.

    e.g.:

    <?php
    if ($objType == 'canine') {
      use     Animal\Canine as Beast;
    }
    if (    $objType == 'bovine') {
      use     Animal\Bovine as Beast;
    }

    $oBeast = new Beast;
    $oBeast->feed();
    ?>
    up
    -3
    kelerest123 at gmail dot com
    9 years ago
    For the fifth example (example #5):

    When in block scope, it is not an illegal use of use keyword, because it is used for sharing things with traits.
    up
    -7
    Anonymous
    11 years ago
    The last example on this page shows a possibly incorrect attempt of aliasing, but it is totally correct to import a trait \Languages\Languages\Danish.
    up
    -4
    dominic_mayers at yahoo dot com
    8 years ago
    To clarify the distinction between inserting a trait in a class and importing a trait in a namespace, here is an example where we first import and then insert a trait.

    <?php
    namespace ns1;
    trait     T {
      static     $a = "In T";
    }

    namespace     ns2;
    use     ns1\T; // Importing the name of trait ns1\T  in the namespace ns2
    class C {
      use     T; // Inserting trait T in the class C, making use of the imported name.
    } 

    namespace     main;
    use     ns2\C;
    echo     C::$a; // In T;
    up
    -3
    info at ensostudio dot ru
    4 years ago
    Note: you can import not existed items without errors:
    <?php
    use UndefinedClass;
    use function     undefined_fn;
    use const     UNDEFINED_CONST;
    ?>
    but you cant use/call they:
    <?php
    $new UndefinedClass    ; // Error: Use of undefined class
    use function undefined_fn; // Error: Use of undefined function
    use const UNDEFINED_CONST; // Error: Use of undefined constant
    ?>
    up
    -12
    Joey
    6 years ago
    For those hoping for an easy fix of DRY with {} unfortunately you can't nest it or do anything cool with it. In case you can only have one per use and if you don't have one then the whole use is assumed to be wrapped in brackets. That means if you do have one you can't use , as normal with use!

    Not possible:

        use A\B\C\{
                D, E,
                F\{X, Y, Z}
            },
            X\Y\Z,
            H\{
                I\{
                    Y\Y\Y\Y\Y,
                    Z, H, E
                },
                J\{
                    A\{
                        G\H\J
                        B\N
                    },
                    G\H\J
                }
            };
    up
    -15
    www.codewars.com
    5 years ago
    amazing!!

    use function strval as numberToString;

    var_dump(numberToString(123));

    //print
    //string(3) "123"
    up
    -9
    Dhairya Lakhera
    5 years ago
    namespace test{

        use test\xyz\tikku;
        use test\xyz\tikku as class_alias;
        use function test\xyz\tikku\foo;
        use function test\xyz\tikku\foo as func_alias;
        use const test\xyz\tikku\ABC;
        use const test\xyz\tikku\ABC as const_alias;
       

       

        $obj=new tikku;
        $obj->Display();  // I am in  test\xyz namespace

        $obj=new tikku\dhairya;
        $obj->Display();   // I am in test\xyz\tikku namespace

        $obj=new class_alias\dhairya;
        $obj->Display();   // I am in test\xyz\tikku namespace

        $obj=new \class_alias\dhairya;
        $obj->Display();  // I am in class_alias namespace

    }

    namespace test\xyz{

       class tikku{
        function Display(){
            echo "I am in ".__namespace__." namespace<br/><hr/>";
        }
       }
    }

    namespace test\xyz\tikku{

       class dhairya{
        function Display(){
            echo "I am in ".__namespace__." namespace<br/><hr/>";
        }
       }
    }

    namespace class_alias{

       class dhairya{
        function Display(){
            echo "I am in ".__namespace__." namespace<br/><hr/>";
        }
       }
    }
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