compact()参数有两种

• 变量名的字符串形式

• 数组的变量名

变量名的字符串

$city  = "San Francisco";
$state = "CA";
$event = "SIGGRAPH";
$location=["city",'state'];
$result=compact('city','state','event','location');
print_r($result)

结果

[
     "city" => "San Francisco",
     "state" => "CA",
     "event" => "SIGGRAPH",
     "location" => [
       "city",
       "state",
     ],
   ]

理解：把变量名的字符串形式传入compact函数，最终结果会输出一个数组，键名为变量名的字符串形式，键值为变量名对应的值

数组的变量名

$city="San Francisco";
$state="CA";
$event = "SIGGRAPH";
$location=["city",'state'];
$result=compact('event',$location);
print_r($result);

结果

[
     "event" => "SIGGRAPH",
     "city" => "San Francisco",
     "state" => "CA",
   ]

理解：直接把数组的变量名传入compact函数，相当于递归，即compact($location)相当于compact(‘city’,’state’)