php function to unset variables passed by reference

Question

currently i'm using this php function :

function if_exist(&$argument, $default = '')
{
    if (isset ($argument))
    {
        echo $argument;
    }
    else
    {
        echo $default;
    }
}

i want this function to unset the variables $argument(passed by reference) and $default just after echoing their value, how can i do this? Thanks in advance.

Answer 1

According to the manual for unset:

If a variable that is PASSED BY REFERENCE is unset() inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset() was called.

I assume this is the issue you're encountering. So, my suggestion is to simply set $argument to NULL. Which, according to the NULL docs will "remove the variable and unset its value.".

For example: $argument = NULL;

Answer 2

$default is passed by value, so it cannot be unset (except in the local scope).

As you undoubtedly discovered, unset() simply unsets the reference to $argument. You can (sort of) unset $argument like this:

$argument = null;