Introduced in PHP 7, the Spaceship operator <=> is used to compare two expressions.
It returns:
- 0 if both values are equal
- 1 if left operand is greater
- -1 if right operand is greater
Let’s see it with an example:
echo 2 <=> 2; // Outputs 0 echo 3 <=> 1; // Outputs 1 echo 1 <=> 3; // Outputs -1 echo "b" <=> "b"; // Outputs 0 echo "a" <=> "c"; // Outputs -1 echo "c" <=> "a"; // Outputs 1 // Note: for string comparison, the ASCII value of the characters are used, that is why "c" is greater than "a" echo "ping" <=> "pong"; // Outputs -1 since "o" is greater than "i" This operator can be used for sorting arrays:
$numbers = [1, 4, 5, 9, 2, 3]; usort($numbers, function ($a, $b) { return $a <=> $b; // Sort in ascending order }); echo print_r($numbers); // Outputs [1,2,3,4,5,9] usort($numbers, function ($a, $b) { return $b <=> $a; // Sort in descending order }); echo print_r($numbers); // [9,5,4,3,2,1] 
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