# PHP Spaceship Operator (<=>)

The spaceship operator (`<=>`) was introduced in PHP 7. It is a three-way comparison operator that returns an integer less than, equal to, or greater than zero when `$a` is respectively less than, equal to, or greater than `$b`.

---

## 1. How it Works
The operator returns:
*   `-1` if the left operand is less than the right.
*   `0` if both operands are equal.
*   `1` if the left operand is greater than the right.

It can be used to compare integers, floats, and strings.

## 2. Examples

### Integers
```php
// Integers
echo 1 <=> 1; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1
```

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

## 3. Use Case: Sorting
The spaceship operator is particularly useful for writing sorting callbacks, for example with `usort()`.

```php
$numbers = [3, 1, 4, 1, 5, 9];

usort($numbers, function ($a, $b) {
    return $a <=> $b;
});

print_r($numbers);
// Array ( [0] => 1 [1] => 1 [2] => 3 [3] => 4 [4] => 5 [5] => 9 )
```

[[programming/php/php]] [[programming/php/php-operators]]