What are the potential issues when upgrading an old PHP script to PHP 7.3?

One potential issue when upgrading an old PHP script to PHP 7.3 is deprecated features or functions that are no longer supported in the newer version. To solve this, you will need to update the deprecated code to use the recommended alternatives or rewrite the code using modern PHP practices. 

// Deprecated code using create_function
$func = create_function('$a,$b', 'return $a + $b;');

// Updated code using anonymous functions
$func = function($a, $b) {
    return $a + $b;
};

Keywords

Deprecated functions backward incompatible changes error reporting compatibility issues performance improvements

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