php匿名函数中的use有什么用

<?php
$msg = [1,2,3];
$func = function()use($msg){
    print_r($msg);
};  

$func();
?>

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)

<?php
$func = function()use($msg){
    print_r($msg);
};  

$msg = [1,2,3];

$func();
?>

PHP Notice:  Undefined variable: msg in /search/ballqiu/c.php on line 4

<?php
$msg = [1,2,3];
$func = function()use(&$msg){
    $msg[0]++;
    print_r($msg);
};


$func();

print_r($msg);
?>

Array
(
    [0] => 2
    [1] => 2
    [2] => 3
)
Array
(
    [0] => 2
    [1] => 2
    [2] => 3
)

<?php
$msg = new ArrayObject([1,2,3], ArrayObject::ARRAY_AS_PROPS);
$func = function()use($msg){
    $msg[0]++;
    print_r($msg);
};

$func();
print_r($msg);
?>

ArrayObject Object
(
    [storage:ArrayObject:private] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 3
        )

)
ArrayObject Object
(
    [storage:ArrayObject:private] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 3
        )

)

<?php
$func = function()use($msg){
    echo $msg[0],"\n";
};

$msg = new ArrayObject([1,2,3], ArrayObject::ARRAY_AS_PROPS);
$func();
?>

$func = function()use(&$msg){
    echo $msg[0],"\n";
};

运行输出1

<?phpclass C{
    protected $_num = 0;    public function mkFunc(){
        $func = function(){
            echo $this->_num++, "\n";
        };        return $func;
    }    public function get(){
        echo $this->_num,"\n";
    }
}$obj = new C();$func = $obj->mkFunc();$func();$obj->get();?>
运行结果01

public function mkFunc(){
    //唯一改动是此处加了use
    $func = function()use($this){
        echo $this->_num++, "\n";
    };    return $func;
}

运行输出
PHP Fatal error:  Cannot use $this as lexical variable

public function mkFunc(){
    $self = $this;    $func = function()use($self){
        echo $this->_num++, "\n";
    };    return $func;
}

运行结果01