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'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;