switch() Revelation

[iceman2g]

$var[x] = 'none';
$var[y] = '';
$var[z] = 'z';

if(empty($var[y]) && empty($var[z]))
	{
	echo 'var[y] & var[z]cannot both be empty';
	}

/* this the same as using above*/
switch(empty($var))
		{		
		case $var[y] || $var[z]:
		echo 'var[y] & var[z]cannot both be empty';
		break;		
		default:
		echo "all variables set";
		break;		
		}

Is there a reason || in the switch is acting as && in above if statement?

I also noticed && in the switch has the same effect as || in our if statement.

I could be doing something wrong. 😕

[terfle]

try this...

$var[x] = 'none';
$var[y] = '';
$var[z] = 'z';

if(empty($var[y]) && empty($var[z]))
    {
    echo 'var[y] & var[z]cannot both be empty';
    }

/* this the same as using above*/
switch(empty($var))
        {        

        case $var[y]:
        case $var[z]:
        echo 'var[y] & var[z]cannot both be empty';
        break;        

        default:
        echo "all variables set";
        break;        

        }

[Drakla]

Shouldn't you be using $var['z'], $var['x'] unless you've defined z and x as constants somewhere?

[laserlight]

empty() returns a boolean value.

empty($var['y']) = true
empty($var['z']) = false
true && false = false

$var is not empty, so
empty($var) = false

But now recall that strings that are not empty or "0" evaluate to true:
$var['z'] = true => $var['y'] || $var['z'] = true

Your switch selection structure now becomes:

switch (false) {
case true:
	echo 'var[y] & var[z]cannot both be empty';
	break;
default:
	echo "all variables set";
}

Clearly control is passed to the default case.

[mtmosier]

First up, these aren't the same. When you did this

case $var[y] || $var[z]:

You are only checking whether the values $var[y] and $var[z] are true or false, you're not checking with empty. Since an empty value does get cast to boolean false this works, but it's not the same. Turn on error notices and don't set one of these (instead of just setting it to empty string), and you will see the difference.

switch(empty($var))

Here you checked whether the $var variable is empty, which you didn't do in the first part at all. Anyway, since in your example $var is never empty, this is always false. So you're checking your case statements against boolean false. That negates the logic. That's why you're && and || get reversed. Logically the following is correct.

!$a && !$b === !($a || $b)
$a || $b === !(!$a && !$b)

In case you didn't catch it, empty is in effect negating the logical boolean value of a variable. And with the case statements comparing to false, you end up in the first situation, !$a && !$b being equivalent to !($a || $b).

For fun try commenting out the $var lines at the beginning altogether.

[laserlight]

terfle, there's no point using a switch for this.
The switch selection structure is best used when you want to compare a certain value with several other values.
Here there are only 2 possible values - true or false.
An if-statement works best.

Not only that, but one runs the risk of an incorrect conversion from the if-statement to a switch (as I believe you have done).
There's really no point in using the switch here.