What does the double not operator do in PHP?
For example:
return !! $row;
What would the code above do?
php
operators
Answers
2
You could make functions that wrap the operators, or for simplicity just use the bc extension:
$operator = '+';
$operators = array(
'+' => 'bcadd',
'-' => 'bcsub',
'*' => 'bcmul',
'/' => 'bcdiv'
);
foreach($resultSet as $item){
$result = call_user_func($operators[$operator], $item[$this->orderField], 1);
echo $result;
}
Wednesday, December 7, 2022
1
There is no "better" but the more common one is ||. They have different precedence and || would work like one would expect normally.
See also: Logical operators (the following example is taken from there):
// The result of the expression (false || true) is assigned to $e
// Acts like: ($e = (false || true))
$e = false || true;
// The constant false is assigned to $f and then true is ignored
// Acts like: (($f = false) or true)
$f = false or true;
Friday, November 11, 2022
3
It is an E4X operator.
From https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide:Processing_XML_with_E4X:
While the . operator accesses direct children of the given node, the .. operator accesses all children no matter how deeply nested:
Saturday, November 19, 2022
3
They behave identically, to the point of producing identical byte code; they're equally efficient. That said, element not in list is usually considered preferred. PEP8 doesn't have a specific recommendation on not ... in vs. ... not in, but it does for not ... is vs. ... is not, and it prefers the latter:
Use
is notoperator rather thannot ... is. While both expressions are functionally identical, the former is more readable and preferred.
To show equivalence in performance, a quick byte code inspection:
>>> import dis
>>> dis.dis('not x in y')
1 0 LOAD_NAME 0 (x)
2 LOAD_NAME 1 (y)
4 COMPARE_OP 7 (not in)
6 RETURN_VALUE
>>> dis.dis('x not in y')
1 0 LOAD_NAME 0 (x)
2 LOAD_NAME 1 (y)
4 COMPARE_OP 7 (not in)
6 RETURN_VALUE
Saturday, August 6, 2022
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operators
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 valueFALSE.It is functionally equivalent to a cast to
boolean: