Analysis and Solutions for the Deprecation of Assigning New Return Values by Reference in PHP

Problem Phenomenon and Technical Background

In PHP version 5.2, developers may encounter the warning message "Assigning the return value of new by reference is deprecated" when instantiating objects. This warning typically appears in scenarios combining the reference assignment operator & with the new keyword.

Code Examples and Problem Analysis

Consider the following code snippet:

$obj_md =& new MDB2();

During the PHP4 era, this syntax was necessary because object assignment defaulted to value copying. However, in PHP5, object assignment defaults to reference mechanisms, making the explicit use of the reference operator redundant and marked as deprecated.

PHP Version Evolution and Reference Mechanism Changes

There are fundamental differences in object handling mechanisms between PHP4 and PHP5. In PHP4, object variables stored copies of objects, necessitating reference assignment to ensure multiple variables pointed to the same object instance:

// PHP4 Required Syntax
$obj1 =& new MyClass();
$obj2 =& $obj1; // Ensure pointing to the same object

In PHP5, object variables store references to objects, allowing the same functionality to be achieved with more concise syntax:

// PHP5 Recommended Syntax
$obj1 = new MyClass();
$obj2 = $obj1; // Automatically references the same object

Solutions and Practical Recommendations

The most direct method to resolve this deprecation warning is to remove the unnecessary reference operator:

// Before correction (generates warning)
$obj_md =& new MDB2();

// After correction (no warning)
$obj_md = new MDB2();

In practical projects, third-party libraries like SimplePie may contain numerous instances of this syntax. Developers need to systematically inspect codebases, replacing all =& new instances with = new.

Error Handling and Compatibility Considerations

While adjusting error_reporting settings can temporarily suppress warnings, this is not a fundamental solution. The correct approach is to fix the code syntax to ensure compatibility with PHP5 and subsequent versions. For legacy system migration, a gradual refactoring strategy is recommended, prioritizing high-frequency core modules.

Technical Evolution Insights

This syntactic change reflects the maturation process of PHP language design. The object model refactoring from PHP4 to PHP5 demonstrates continuous attention to developer experience and performance optimization from language designers. Understanding these underlying mechanism changes helps developers better grasp language evolution trends and write more robust and maintainable code.