php array_map回调参数范围 [英] php array_map callback parameter scope

问题描述

在以下代码中，传递给wrap_map的回调函数在外部函数中看不到参数，为什么? (有关详细信息，请参见代码注释)

In the following code the callback function passed to wrap_map can't see the argument in the outer function, why? (see code comment for detail)

public static function wrap_implode($ar, $wrap, $delim){
  echo "wrap is $wrap"; //wrap is ok
  $res = array_map(function($val){
     echo "wrap is $wrap"; //wrap is not set here!
     return $wrap. $val . $wrap;
   }, $ar);

   return implode($delim, $res);
}

推荐答案

因为它在另一个作用域中.如果要使用$wrap，请尝试:

Because it is in another scope. If you want to use $wrap, try:

function($val) use ($wrap){
   //etc
}

当然，这里的函数不需要回调:

Of course, your function here doesn't need a callback:

return $wrap.implode($wrap.$delim.$wrap,$ar).$wrap;

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