什么是控制变量绑定在闭包中的php设置？

Question

the following two pieces work on two separate machines.
Both machines are php5.5.x (not sure what is x).
i.e. one work on one machine only and the other one on both (the one with use).
Notice the use of the keyword **use** in the second version. Sadly, I have no command line access to those machines to check php settings.
version one

$a = 1;
$b = function(){
   echo $a;
};
$b();

version two:

$a = 1;
$b = function() use($a){
   echo $a;
};
$b();

Answer 1

Your first closure is experiencing a variable scope issue, $a does not exist inside the closure. You can fix this by:

1. defining global $a inside of the closure.
2. Use the use keyword as in your second example.
   • Only available in PHP version >= 5.3
3. Use arguments instead
   • echo (function($a){ echo $a; })("test");

You should enable error reporting to see why your first closure should not work in the first place

ini_set("display_errors", 1);
error_reporting(-1);

$a = 1;
$b = function(){
  echo $a; // Notice: Undefined variable: a in /path/to/script.php on line #
};
$b();

If both hosts are running PHP 5.5, the output should be the same. It might be that 1 is suppressing the notice messages and the other is not. If that's the case, the ini settings you should be looking for are:

error_reporting
display_errors

And as shown above, you can simply change those settings at script run-time by using ini_set() where error_reporting(-1) is a simple shortcut to ini_set('error_reporting', E_ALL | E_STRICT)