Yesterday I stumbled over this when I modified PHP code written by someone else. I was baffled that a simple comparison ( if ($var ==! " ") ) didn't work as expected. After some testing I realized that whoever wrote that code used ==! instead of !== as comparison operator. I've never seen ==! in any language so I wondered how the hell this code could even work and did some testing:

<?php
echo "intn";
echo "1 !== 0: "; var_dump(1 !== 0);
echo "1 !== 1: "; var_dump(1 !== 1);
echo "1 ==! 0: "; var_dump(1 ==! 0);
echo "1 ==! 1: "; var_dump(1 ==! 1);
echo "booln";
echo "true !== false: "; var_dump(true !== false);
echo "true !== true: "; var_dump(true !== true);
echo "true ==! false: "; var_dump(true ==! false);
echo "true ==! true: "; var_dump(true ==! true);
echo "stringn";
echo '"a" !== " ": '; var_dump("a" !== " ");
echo '"a" !== "a": '; var_dump("a" !== "a");
echo '"a" ==! " ": '; var_dump("a" ==! " ");
echo '"a" ==! "a": '; var_dump("a" ==! "a");
?>

This produces this output:

int
1 !== 0: bool(true)
1 !== 1: bool(false)
1 ==! 0: bool(true)
1 ==! 1: bool(false)
bool
true !== false: bool(true)
true !== true: bool(false)
true ==! false: bool(true)
true ==! true: bool(false)
string
"a" !== " ": bool(true)
"a" !== "a": bool(false)
"a" ==! " ": bool(false)
"a" ==! "a": bool(false)

The operator seems to work for boolean and integer variables, but not for strings. I can't find ==! in the PHP documentation or anything about it on any search engine (tried Google, Bing, DuckDuckGo, but I suspect they try to interpret it instead of searching for the literal string). Has anybody seen this before and can shed any light on this behavior?

---

The difference is that there is no operator ==! .

This expression:

$a ==! $b

Is basically the same as this:

$a == (!$b)

---

There is no ==! operator in PHP

Its just a combination of == and ! . Only relevant operator present here is == . So the combination ==! will work just as a normal == , checking Equality , and trust me,

$variable_a ==! $variable_b 

is none other than

$variable_a == (!$variable_b)

and thus;

"a" ==! " ": bool(false)
"a" ==! "a": bool(false) //is same as "a" == (!"a")

And

true ==! false: bool(true)
true ==! true: bool(false)

Combining multiple operators characters may not work as an operator always. for example, if we take = and ! , it will work as operators only if it is in the pattern of != or !== . There can be numerous combinations for these characters like !==== , !==! etc.. etc.. Operator combinations should be in unique format , unique order , unique combinations (all characters wont combine with all other characters) and definitely, without any space between them .

Check the operators list below;

---

==! is not an operator but two :

== and !

! having a higher priority than ==

So :

"a" !== " ": bool(true) --> true because "a" is really not equal to " "

"a" ==! " ": bool(false) "a" ==! " ": bool(false) --> false because "a" is not equals to !" "

Could be written with a space between == and !.

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