I've tested the following and it works on both PHP 5.2 and 5.3, however, it's not documented anywhere as far as I can see so I'm evaluating its use.
I have a function in a class called isValid, this checks a hash to see if the given value is in the set of allowed values. There are some values that are valid, but deprecated; I'd like my isValid function to update the passed in value to the current one and return true.
That's fine for when I call it myself, however, I'd like to use this method when used as a callback for array_filter too.
Here's a test case, which as expected results in an array with the values 2,3,4,5,6.
<?php
$test = array(1, 2, 3, 4, 5);
echo print_r(array_filter($test, 'maptest'), true);
function maptest(&$value)
{
$value ++;
return true;
}
So StackOverflow: is this allowed, or is it undocumented functionality that may disappear/stop working/cause errors in the future?
Yes, it's allowed.
In this respect, there's nothing special about calling functions through callbacks.
However, your specific example does not illustrate one difficulty. Consider:
function inc(&$i) { $i++; }
$n = 0;
// Warning: Parameter 1 to inc() expected to be a reference, value given:
call_user_func('inc', $n);
The problem is that you're passing $n
to call_user_func
and call_user_func
doesn't accept values by reference. So by the time inc
is called, it won't receive a reference. This isn't a problem with array_filter
because it traverses the array directly and can directly pass the variables in the array to the callback function.
You could use call-time pass-by-reference, but this is deprecated and removed from trunk:
function inc(&$i) { $i++; }
$n = 0;
// Deprecated: Call-time pass-by-reference has been deprecated
call_user_func('inc', &$n);
So the best option is to use call_user_func_array
instead:
function inc(&$i) { $i++; }
$n = 0;
call_user_func_array('inc', array(&$n));
This function will pass-by-reference the elements that have the is_ref
flag set and will pass-by-value the other ones.
Except when explicitly noted, I'd say this is fine and acceptable. A callback can be any built-in or user-defined function.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With