Recipe 6.4 Passing Values by Reference
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.
6.4.4 See Also
Recipe 6.7 on returning values by reference.
|
