[英]What is Closure::bind() in PHP
The PHP manual offers little explanation about Closure::bind() and the example was confusing too. PHP手册没有提供关于Closure :: bind()的解释,这个例子也令人困惑。
Here's the code example on the site: 这是网站上的代码示例:
class A {
private static $sfoo = 1;
private $ifoo = 2;
}
$cl1 = static function() {
return A::$sfoo;
};
$cl2 = function() {
return $this->ifoo;
};
$bcl1 = Closure::bind($cl1, null, 'A');
$bcl2 = Closure::bind($cl2, new A(), 'A');
echo $bcl1(), "\n";
echo $bcl2(), "\n";
What are the parameters for Closure::bind()? Closure :: bind()的参数是什么?
Null was used in the above, and even the "new" keyword was used too, which makes this even more confusing to me. 上面使用了Null,甚至使用了“new”关键字,这让我更加困惑。
If you put the value of $cl2
as a method of class A
, the class looks like this: 如果将
$cl2
的值作为类A
的方法,则该类如下所示:
class A {
public $ifoo = 2;
function cl2()
{
return $this->ifoo;
}
}
and you can use it like this: 你可以像这样使用它:
$x = new A();
$x->cl2();
# it prints
2
But, because $cl2
is a closure and not a member of class A
, the usage code above does not work. 但是,因为
$cl2
是一个闭包而不是A
类的成员,所以上面的用法代码不起作用。
The method Closure::bindTo()
allows using the closure as it were a method of class A
: Closure::bindTo()
允许使用闭包,因为它是A
类的方法:
$cl2 = function() {
return $this->ifoo;
};
$x = new A();
$cl3 = $cl2->bindTo($x);
echo $cl3();
# it prints 2
$x->ifoo = 4;
echo $cl3();
# it prints 4 now
The closure uses the value of $this
but $this
is not defined in $cl2
. 闭包使用
$this
的值但$this
未在$cl2
定义。 When $cl2()
runs, $this
is NULL
and it triggers an error ( "PHP Fatal error: Using $this
when not in object context" ). 当
$cl2()
运行时, $this
为NULL
并且它会触发错误( “PHP致命错误:在不在对象上下文中时使用$this
” )。
Closure::bindTo()
creates a new closure but it "binds" the value of $this
inside this new closure to the object it receives as its first argument. Closure::bindTo()
创建一个新的闭包,但它将这个新闭包内的$this
的值“绑定”到它接收的对象作为其第一个参数。
Inside the code stored in $cl3
, $this
has the same value as the global variable $x
. 在
$cl3
存储的代码中, $this
与全局变量$x
具有相同的值。 When $cl3()
runs, $this->ifoo
is the value of ifoo
in object $x
. 当
$cl3()
运行时, $this->ifoo
是对象$x
中ifoo
的值。
Closure::bind()
is the static version of Closure::bindTo()
. Closure::bind()
是Closure::bindTo()
的静态版本。 It has the same behaviour as Closure::bindTo()
but requires an additional argument: the first argument must be the closure to bind. 它与
Closure::bindTo()
具有相同的行为,但需要一个额外的参数:第一个参数必须是要绑定的闭包。
If you prefer to use static version, just try to 如果您更喜欢使用静态版本,请尝试
$cl4 = Closure::bind(function () { return $this->ifoo; }, new A(), 'A');
echo $cl4();
// it returns "2"
It is pretty cool, if you wanna update the property of an object, but there is no 'setter' for the property. 如果你想更新一个对象的属性,它很酷,但是没有'setter'属性。 For example:
例如:
class Product {
private $name;
private $local;
public function __construct(string $name) {
$this->name = $name;
$this->local = 'usa':
}
}
$product1 = new Product('nice product');
echo $product1->local;
// it returns 'usa'
$product2 = \Closure::bind(function () {
$this->local = 'germany';
return $this;
}, new Product('nice product'), 'Product');
echo $product2->local;
// it returns 'germany'
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