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 "int\n";
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 "bool\n";
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 "string\n";
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)