我什么时候应该在 '$this' 上使用 'self'? [英] When should I use 'self' over '$this'?

问题描述

在 PHP 5 中，使用 self 和 $this 有什么区别?

什么时候合适?

解决方案

简答

<块引用>

使用 $this 来引用当前目的.使用 self 来引用当前班级.换句话说，使用$this->member 用于非静态成员，将 self::$member 用于静态成员.

完整答案

以下是$this 和self 用于非静态和静态成员变量的正确用法示例:

non_static_member .' '.self::$static_member;}}新的 X();?>

这里是一个不正确使用$this和self用于非静态和静态成员变量的例子:

static_member;}}新的 X();?>

这里是一个多态的例子，$this用于成员函数:

foo();}}Y 类扩展 X {函数 foo() {echo 'Y::foo()';}}$x = 新 Y();$x->bar();?>

以下是一个通过对成员函数使用 self 来抑制多态行为的示例:

bar();?>

<块引用>

这个想法是 $this->foo() 调用 foo() 成员函数，无论当前对象的确切类型是什么.如果对象是type X，它就会调用X::foo().如果对象是type Y，它会调用Y::foo().但是对于 self::foo()，X::foo() 总是被调用.

来自 http://www.phpbuilder.com/board/showthread.php?t=10354489:

由 http://board.phpbuilder.com/member.php?145249-laserlight

In PHP 5, what is the difference between using self and $this?

When is each appropriate?

解决方案

Short Answer

Use $this to refer to the current object. Use self to refer to the current class. In other words, use $this->member for non-static members, use self::$member for static members.

Full Answer

Here is an example of correct usage of $this and self for non-static and static member variables:

<?php
class X {
    private $non_static_member = 1;
    private static $static_member = 2;

    function __construct() {
        echo $this->non_static_member . ' '
           . self::$static_member;
    }
}

new X();
?>

Here is an example of incorrect usage of $this and self for non-static and static member variables:

<?php
class X {
    private $non_static_member = 1;
    private static $static_member = 2;

    function __construct() {
        echo self::$non_static_member . ' '
           . $this->static_member;
    }
}

new X();
?>

Here is an example of polymorphism with $this for member functions:

<?php
class X {
    function foo() {
        echo 'X::foo()';
    }

    function bar() {
        $this->foo();
    }
}

class Y extends X {
    function foo() {
        echo 'Y::foo()';
    }
}

$x = new Y();
$x->bar();
?>

Here is an example of suppressing polymorphic behaviour by using self for member functions:

<?php
class X {
    function foo() {
        echo 'X::foo()';
    }

    function bar() {
        self::foo();
    }
}

class Y extends X {
    function foo() {
        echo 'Y::foo()';
    }
}

$x = new Y();
$x->bar();
?>

The idea is that $this->foo() calls the foo() member function of whatever is the exact type of the current object. If the object is of type X, it thus calls X::foo(). If the object is of type Y, it calls Y::foo(). But with self::foo(), X::foo() is always called.

From http://www.phpbuilder.com/board/showthread.php?t=10354489:

By http://board.phpbuilder.com/member.php?145249-laserlight

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