Double not (!!) operator in PHP
What does the double not operator do in PHP?
For example:
return !! $row;
What would the code above do?
It's not the "double not operator", it's the not operator applied twice. The right ! will result in a boolean, regardless of the operand. Then the left ! will negate that boolean.
This means that for any true value (numbers other than zero, non-empty strings and arrays, etc.) you will get the boolean value TRUE , and for any false value (0, 0.0, NULL , empty strings or empty arrays) you will get the boolean value FALSE .
It is functionally equivalent to a cast to boolean :
return (bool)$row;
It's the same (or almost the same - there might be some corner case) as casting to bool. If $row would cast to true, then !! $row !! $row is also true.
But if you want to achieve (bool) $row , you should probably use just that - and not some "interesting" expressions ;)
It means if $row has a truthy value, it will return true , otherwise false , converting to a boolean value.
Here is example expressions to boolean conversion from php docs.
Expression Boolean
$x = ""; FALSE
$x = null; FALSE
var $x; FALSE
$x is undefined FALSE
$x = array(); FALSE
$x = array('a', 'b'); TRUE
$x = false; FALSE
$x = true; TRUE
$x = 1; TRUE
$x = 42; TRUE
$x = 0; FALSE
$x = -1; TRUE
$x = "1"; TRUE
$x = "0"; FALSE
$x = "-1"; TRUE
$x = "php"; TRUE
$x = "true"; TRUE
$x = "false"; TRUE
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