How to use bind() and bindTo() of PHP Closure class?

See the PHP manual for usage of Closure’s bind and bindTo. I really don't understand it and don't understand the concept.
For example, Closure::bind, the manual says "copy a closure and bind the specified $this object and class scope". How to understand this?
How are closures and $this bound together? What is class scope used for?
Also, one is a static version and the other is a dynamic version. What does this refer to?
Can you explain these concepts using the examples given?

<code><?php
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";
?></code>

Thank you

Reply content:

See the PHP manual for usage of Closure’s bind and bindTo. I really don't understand it and don't understand the concept.
For example, Closure::bind, the manual says "copy a closure and bind the specified $this object and class scope". How to understand this?
How are closures and $this bound together? What is class scope used for?
Also, one is a static version and the other is a dynamic version. What does this refer to?
Can you explain these concepts using the examples given?

<code><?php
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";
?></code>

Thank you

I don’t know if you have ever used call or apply ​​in js, which is somewhat similar.

In fact, the closure is treated as a member method or static member method of the object.

Closure::bind($cl1, null, 'A'); //就相当于在类里面加了个静态成员方法
Closure::bind($cl2, new A(), 'A'); //相当于在类里面加了个成员方法

Member methods use $this to access objects, and static member methods directly use classname::membermethod.
But because it is an anonymous function and has no function name, it returns a bound $this object and class function. The closure of the domain is for you to use.