6.4.1 Problem
You want to pass a variable to a
function and have it retain any changes made to its value inside the function.
6.4.2 Solution
To instruct a function to accept an argument passed by
reference instead of value, prepend an & to
the parameter name in the function prototype:
function wrap_html_tag(&$string, $tag = 'b') {
$string = "<$tag>$string</$tag>";
}
Now there's no need to return the string because the original
is modified in-place.
6.4.3 Discussion
Passing a variable to a function by reference allows you to
avoid the work of returning the variable and assigning the return value to the
original variable. It is also useful when you want a function to return a
boolean success value of true or false, but you still want to
modify argument values with the function.
You can't switch between passing a parameter by value or
reference; it's either one or the other. In other words, there's no way to tell
PHP to optionally treat the variable as a reference or as a value.
Actually, that statement isn't 100% true. If the configuration
directive allow_call_time_pass_reference is
enabled, PHP lets you optionally pass a value by reference by prepending an
ampersand to the variable's name. However, this feature has been deprecated
since PHP 4.0 Beta 4, and PHP issues explicit warnings that this feature may go
away in the future when you employ call-time pass-by-reference. Caveat coder.
Also, if a parameter is declared to accept a value by
reference, you can't pass a constant string (or number, etc.), or PHP will die
with a fatal error.
