Hi acemaster,

Its called 'Passing by Reference'. It means that both your variables point to the same content. This should help you out:

[uk.php.net...]

dc

Thanks dc, but it doesn't say anywhere about being able to use it as a comparison operator, at least I couldn't find it.

It's not a comparison operator, you are using it as a logical "AND" operator in your code. So if you take this part alone of the if statement $b &= $c is basically $b = $b&$c (logical and assignment)

Yes, as enigma1 states. Not to be confused with the similar looking 'assign/pass' by Reference (=&)

&=

... Logical bitwise AND

=&

... 'assign' by Reference

Just as a matter of interest, have you tried echo'ing the values of $a, $b, $c and $d after your if() statement (if the values are initially different and not equal)? Something like:

$a = "test1"; 
$b = "test2"; 
$c = "test3"; 
$d = "test4"; 
if ($a == $b &= $c &= $d) { 
 echo "true"; 
}else{ 
 echo "false"; 
} 
echo '<br>'; 
echo "$a - $b - $c - $d";

Results in:

false
test1 - test0 - test0 - test4

Which is not what you require. (Bitwise Operators [php.net])

Just expanding on what enigma1 wrote above... The bitwise assignment operators work from right to left, so what your code is actually doing is equivalent to:

$c = $c & $d; 
$b = $b & $c; 
if ($a == $b) { ... 

To check if 4 variables are the same you will need to do something like:

if ($a == ($b == ($c == $d))) { 
 echo "true"; 
} else { 
 echo "false"; 
}

That won't work either. Working from within the parenthesis, $c == $d will return boolean

TRUE

as the value of variable $c which is "test" does indeed equal the value of variable $d which is "test". The return value of that expression is boolean

TRUE

. Now you have ...

if ($a == ($b == ((bool) 
TRUE
))) {

... and so the statement will indeed return true.

if ($a == ($b == ((bool) TRUE))) {

Dang, of course - thanks!

In that case, it's just the usual...

if (($a == $b) && ($b == $c) && ($c == $d)) { 
 echo "true\n"; 
} else { 
 echo "false\n"; 
}

Anything 'quicker'?

IMHO, if you need to check for equality between many variables then I'd use an alternative memory structure eg. an array.

I agree, that was my first thought :)

You could probably get fancy with something like array_diff and array_filter, perhaps array_values thrown in ... just some initial thoughts that raced through my mind.

If you want to use an array_* function, you'd probably want array_unique [us.php.net]:

if (1 == sizeof(array_unique([$a, $b, $c, $d]))) {
 // ...
}

Something like that.