PHP: using empty() for empty string?

Question

I recently discovered this interesting article by Deceze.
But I'm a bit confused by one of its advises:

never use empty or isset for variables that should exist

Using empty() is not good choice to test if $foo = ''; is empty?

Answer 1

What he means is if you want to check if the string is empty then empty won't do that. Empty can mean false, 0, null. Anything 'falsy'.

E.g. these are all true:

<?php

$string = null;
if (empty($string)) {
    echo "This is true";
}

$string = '';
if (empty($string)) {
    echo "This is true";
}

$string = 0;
if (empty($string)) {
    echo "This is true";
}

If you want to check if the string is an empty string you should do this check for '':

<?php 

$string = '';
if (isset($string) && $string === '') {
    echo "This is true";
}

$string = null;
if (isset($string) && $string === '') {
    echo "This is false";
}

Answer 2

You should not use empty (or isset) if you expect $foo to exist. That means, if according to your program logic, $foo should exist at this point:

if ($foo === '')

Then do not do any of these:

if (isset($foo))
if (empty($foo))

These two language constructs suppress error reporting for undefined variables. That's their only job. That means, if you use isset or empty gratuitously, PHP won't tell you about problems in your code. For example:

$foo = $bar;
if (empty($føø)) ...

Hmm, why is this always true, even when $bar contains the expected value? Because you mistyped the variable name and you're checking the value of an undefined variable. Write it like this instead to let PHP help you:

if (!$føø) ...

Notice: undefined variable føø on line ...

The condition itself is the same, == false (!) and empty produce the same outcome for the same values.

How exactly to check for an empty string depends on what values you do or don't accept. Perhaps $foo === '' or strlen($foo) == 0 is the check you're looking for to ensure you have a string with something in it.