PHP 7.3: References in
list() construct is useful to quickly create multiple variables from an array, with array keys being the variable name. Until PHP 7.3, is was not possible to assign the variables by reference. Prior to PHP 7.3, the following snippet would throw a fatal error:
$arr = ['apple', 'orange']; list($a, &$b) = $arr; $b = 'banana'; echo $arr; // Fatal error:  and list() assignments cannot be by reference in .. on line ..
With PHP 7.3, you will be able do so, and the output from
echo $arr will be
[$a, &$b] = $arr syntax will get this feature too.
You still cannot reference non-referencable variables:
list($a, &$b) = [12, 14] will throw:
Fatal error: Cannot assign reference to non referencable value in .. on line ...
Minor nitpick: while "referencable" is an acceptable spelling, "referenceable" is used a lot more widely.
Backwards compatibility impact
None. Instead of using
list() assignment to populate multiple variables, I would suggest you to use value objects to make things cleaner. They will be passed by reference anyway and will make your code much cleaner.