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PHP Error: Cannot Reassign Non-Variable References – How to Fix It

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1. Introduction to Fixing PHP "Cannot Reassign Non-Variable References" Error

In PHP, when you attempt to reassign a non-variable reference, you might encounter an error like: "Cannot re-assign $foo, not a variable reference." This error indicates that you're trying to assign a reference to something that isn't a variable, causing PHP to throw an error and halt the execution. This article will help you understand and fix this issue, ensuring you can use references correctly in PHP.

2. Basics of References

In PHP, a reference is a pointer to a variable that allows us to modify its value from different locations. By using references, you can directly change the value of a variable without creating a copy of it. Below is a simple example of how references work:


  $a = 10;
  $b = &$a;
  $b = 5; // $a is now 5

In the example above, we assign the value 10 to $a, then set $b as a reference to $a. Now, when $b is modified, $a's value will also change accordingly.

3.1 Why the "Cannot Reassign Non-Variable References" Error Happens

In PHP, if you try to assign a reference to a constant or another immutable data type, you'll encounter the "Cannot reassign non-variable references" error. The following code demonstrates this situation:


  $a = 10;
  $b = 20;
  $c = &$a;
  $c = $b; // Error: Cannot reassign reference
  $d = &$c;
  $d = 30;
  echo $a; // Outputs: 30
  echo $b; // Outputs: 20

This code shows that when we try to assign a non-reference variable ($b) to a reference variable ($c), PHP will throw an error. This will cause the program to stop executing.

3.2 Solution

To resolve this error, ensure that you declare a variable before assigning a reference to it. If a variable is not declared before being referenced, PHP will throw a fatal error. Also, use the "&" symbol to mark variables as references, ensuring they are mutable. Below is a corrected version of the code:


  $a = 10;
  $b = 20;
  $c = &$a;
  $c = $b;
  $d = &$c;
  $d = 30;
  echo $a; // Outputs: 30
  echo $b; // Outputs: 20

In this corrected version, references are used correctly, and variables are properly declared before use, thus avoiding the error.

4. Conclusion

References in PHP are a powerful feature that allows you to modify the value of variables and maintain their state during execution. However, when working with references, it’s important to ensure that variables are declared properly and that assignments follow PHP's syntax rules. By following the guidance in this article, you should be able to avoid the "Cannot reassign non-variable references" error and write more efficient and stable PHP code.

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