Cannot re-assign $this?

问题

I have a script on a server that had php version 4. Now it is changed to php5 and the script does not function any more. I get this error:

Fatal error: Cannot re-assign $this in URL database.php line 88

In the file is a class that has a function. Inside is the line 88:

$this = new $db( $serv, $user, $pass, $dbName );

What does the error mean and how can I change it?

回答1:

$this is a special "variable" that always refers to the object the current function is executing in. It only makes sense inside functions that belong to a class; however, you are not allowed to use it anywhere else, and you may never assign to it. The solution is simply to rename the variable.

回答2:

You can reassign $this value by variable variable

$name = 'this';
$$name = 'stack';
echo $this;

// this will result stack

回答3:

The class is attempting to re-define itself ($this in php is the same as this in C#) and it can't be done. You should change $this to something else and the error should be gone then.

回答4:

$this is a reserved variable name and cannot manually be assigned a value.

回答5:

$this is a predefined variable in PHP.

Here's the reference in the PHP manual: Classes and Objects: The Basics. It describes how, inside a method, $this points to "this object" that is being operated upon. It is still reserved outside a method, though.

Change the identifier to another word.

回答6:

You can use refrences trick:

$thisRef = &$this;
$thisRef = new $db($serv, $user, $pass, $dbName);

来源：https://stackoverflow.com/questions/19242647/cannot-re-assign-this