Double not (!!) operator in PHP

Question

What does the double not operator do in PHP?

For example:

return !! $row;

What would the code above do?

Answer 1

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