Is the logical not(!) operator used with an assignment operator to always assign false value to the variable on left side of the assignment operator?

Question

I've following code snippet, please go through it :

<?php
    // Top of the page, before sending out ANY output to the page.
        $user_is_first_timer = !isset( $_COOKIE["FirstTimer"] );

    // Set the cookie so that the message doesn't show again
        setcookie( "FirstTimer", 1, strtotime( '+1 year' ) );
?>

<H1>hi!</h1><br>


<!-- Put this anywhere on your page. -->
<?php if( $user_is_first_timer ): ?>
    Hello there! you're a first time user!.
<?php endif; ?>

In my coding experience, most of the time I've seen statements like !isset( $_COOKIE["FirstTimer"] ) with the if statement. For the first time in my life I'm observing such statement with the assignment operator.

In the above code I only want to understand what does the statement $user_is_first_timer = !isset( $_COOKIE["FirstTimer"] ); do?

What is the role of logical not(!) operator in this code line?

Please clear my doubts with good and reliable explanation.

Thank You.

Answer 1

By example.

Isset (isset: Determine if a variable is set and is not NULL):

$foo = '1';
$bar = '';
$baz = null;

var_dump(isset($foo));
var_dump(isset($bar));
var_dump(isset($baz));
var_dump(isset($bat));

Output:

bool(true)
bool(true)
bool(false)
bool(false)

Not operator:

var_dump(!true);
var_dump(!false);

Output:

bool(false)
bool(true)

Together:

$qux = 'something';
var_dump(!isset($qux));
var_dump(!isset($quux)); // Note quux isn't set.

Output:

bool(false)
bool(true)

So in your example, if the cookie value is not set (!isset), you are concluding they have not visited the site before.

With assignment you can have $true = !false. $true here will hold true, not false.