函数回调（PHP）无法正常工作

Question

When I execute following code I am getting this error. Why is that? What is the proper use of callbacks?

CODE (simplified)

class NODE {
  //...some other stuff
  function create($tags, $callback=false) {
    $temp = new NODE();
    //...code and stuff
    if($callback) $callback($temp); //fixed (from !$callback)
    return $this;
  }
}
$document = new NODE();
$document->create("<p>", function($parent) {
$parent->create("<i>");
});

ERROR

Fatal error: Function name must be a string in P:\htdocs\projects\nif\nif.php on line 36

Answer 1

$document->new NODE();

This is not valid syntax. The accepted format would be:

$document = new NODE();

In addition to this, if you use the unary operator ( ! ) on a false, you get true. If you use it on a Callable , you get false. As such, if (!$callback) $callback() will throw the first error of your script.

As a side note, you are reinventing the wheel. I would strongly recommend you take a look at the DOMDocument family of classes, which are doing exactly what you are currently trying to implement, albeit with fewer callbacks.

Answer 2

if(!$callback) $callback($temp);

should probably be

if($callback) $callback($temp);

And the instanciation:

$document = new NODE();

Answer 3

if(!$callback) $callback($temp);

如果$callback为false ，请确保您无法将其作为回调调用。

Answer 4

My 2c here, type hinting may be good to use here as well.

Ex: function create($tags, callable $callback = function())

Answer 5

To do such a thing in php you should use function pointers and tell php which function to execute. Look at this code.

// This function uses a callback function.
function doIt($callback)
{
    $data = acquireData();
    $callback($data);
}


// This is a sample callback function for doIt().
function myCallback($data)
{
    echo 'Data is: ', $data, "\n";
}


// Call doIt() and pass our sample callback function's name.
doIt('myCallback');  

So as you seen you can only pass the name to the function and you should predefine the function..

Similar question: How do I implement a callback in PHP?