Why is Call-Time Pass-by-Reference Deprecated in PHP and How Can I Fix the Warning?

Call-Time Pass-by-Reference Deprecation in PHP

The provided code triggers the warning "Call-time pass-by-reference has been deprecated." This warning indicates that the use of call-time pass-by-reference, denoted by the & operator before variable references, is no longer supported in PHP.

Call-Time Pass-by-Reference

In older versions of PHP, call-time pass-by-reference allowed simulating the behavior of passing by reference when using pass-by-value functions. This involved prepending the variable reference with & at the call time, e.g.:

not_modified(&$x);

This allowed modifying the variable referenced by $x within the function.

Deprecation

Call-time pass-by-reference has been deprecated in subsequent versions of PHP and should not be used. Instead, variables should be explicitly passed by reference using &, e.g.:

modified($x);

Objects and Pass-by-Reference

In older versions of PHP, objects required pass-by-reference when modified within functions. However, this is no longer necessary in modern PHP versions as objects are always passed by reference by default. Therefore, the use of &$this in the provided code is redundant.

Solution

To resolve the warning, remove all instances of & from the provided code. The following is the updated code:

function XML() {
    $this->parser = xml_parser_create();
    xml_parser_set_option($this->parser, XML_OPTION_CASE_FOLDING, false);
    xml_set_object($this->parser, $this);
    xml_set_element_handler($this->parser, 'open', 'close');
    xml_set_character_data_handler($this->parser, 'data');
}
function destruct() {
    xml_parser_free($this->parser);
}
function parse($data) {
    $this->document = array();
    $this->stack    = array();
    $this->parent   = &$this->document;
    return xml_parse($this->parser, $data, true) ? $this->document : NULL;
}

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