Why is my PHP code generating \'Call-Time Pass-by-Reference is Deprecated\' warnings, and how can I fix them?

Warning: PHP Call-Time Pass-by-Reference is Deprecated

The warning "Call-time pass-by-reference has been deprecated" indicates the usage of an outdated approach to passing variables as references in function calls. Let's explore its cause and resolution.

In PHP, variables can be passed by value or by reference. Passing by value creates a copy of the variable that can't be modified outside the function, while passing by reference allows the function to modify the original variable itself.

In older versions of PHP, "call-time pass-by-reference" allowed simulating reference passing without explicitly using the & operator. This technique involved passing variables with & in function calls, such as not_modified(&$x). However, this practice has been deprecated in modern PHP and should not be used.

Additionally, in PHP 4 and earlier, modifying object properties required passing the object by reference (using &$obj). However, this is no longer necessary or recommended in modern PHP. Objects are always passed by reference implicitly, allowing for modification even when passed "by value."

Therefore, to resolve the warning, remove & from all references in your code. This includes removing & from all instances of &$this, as it is unnecessary and can be removed entirely. By following these recommendations, you will eliminate the warning and ensure compatibility with modern PHP versions.

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