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What is the output of this script?

<?php
$a = "apples" <=> "bananas";
$b = $a ?? $c ?? 10;
echo $b;

-1

apples

<=> Spaceship, An integer less than, equal to, or greater than zero when $a is respectively less than, equal to, or greater than $b. Available as of PHP 7.

// Integers
echo 1 <=> 1; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1

// Strings
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1

echo "a" <=> "aa"; // -1
echo "zz" <=> "aa"; // 1

Null Coalescing Operator ?? available as of PHP 7. The expression (expr1) ?? (expr2) evaluates to expr2 if expr1 is NULL, and expr1 otherwise. In particular, this operator does not emit a notice if the left-hand side value does not exist, just like isset(). This is especially useful on array keys.

<?php

$foo = null;
$bar = null;
$baz = 1;
$qux = 2;

echo $foo ?? $bar ?? $baz ?? $qux; // outputs 1

?>

https://www.php.net/manual/en/language.operators.comparison.php