The spaceship operator () in PHP returns -1, 0, or 1 based on whether the left operand is less than, equal to, or greater than the right operand, making it ideal for sorting callbacks. 2. It simplifies numeric and string comparisons, eliminating verbose if-else logic in usort, uasort, and uksort. 3. When sorting complex data like arrays of associative arrays or objects, it enables clean multi-level sorting by comparing arrays lexicographically, such as returning [$a['age'], $a['name']] [$b['age'], $b['name']] to sort by age then name. 4. It handles mixed types using PHP’s loose comparison rules, so caution is needed with type juggling, but it correctly manages integers and floats. 5. Best practices include chaining comparisons, using null coalescing for missing keys, and implementing it in classes for Comparable-like behavior, resulting in cleaner, more readable, and less error-prone sorting logic.

The spaceship operator () in PHP is a powerful tool that simplifies comparison logic, especially when dealing with sorting. Introduced in PHP 7, it’s officially called the combined comparison operator, and it helps you write cleaner, more readable sorting callbacks—particularly when working with usort, uasort, or uksort.

Here’s how it works and why it makes complex sorting easier.

What Does the Spaceship Operator Do?

The operator compares two values and returns:

• -1 if the left operand is less than the right,
• 0 if they are equal,
• 1 if the left operand is greater than the right.

This three-way comparison is exactly what PHP’s sorting functions expect in their callback functions.

Instead of writing verbose if-else blocks or multiple conditions, you can use to get the correct return value directly.

Example: Simple numeric sort

$numbers = [3, 1, 4, 1, 5];
usort($numbers, function($a, $b) {
    return $a <=> $b; // Ascending order
});
// Result: [1, 1, 3, 4, 5]

Compare that to the old way:

usort($numbers, function($a, $b) {
    if ($a == $b) return 0;
    return ($a < $b) ? -1 : 1;
});

The spaceship version is much more concise and less error-prone.

Sorting Arrays of Objects or Associative Arrays

When sorting more complex data, like an array of associative arrays or objects, the spaceship operator really shines by allowing chained comparisons.

Example: Sort users by age, then by name

$users = [
    ['name' => 'Alice', 'age' => 30],
    ['name' => 'Bob',   'age' => 25],
    ['name' => 'Charlie', 'age' => 30],
];

usort($users, function($a, $b) {
    return [$a['age'], $a['name']] <=> [$b['age'], $b['name']];
});

This sorts first by age, then by name alphabetically if ages are equal. The key trick here is comparing two arrays using <=>. PHP compares them lexicographically: element by element, using the spaceship logic at each step.

Without <=>, you'd need nested conditionals:

if ($a['age'] != $b['age']) {
    return $a['age'] < $b['age'] ? -1 : 1;
}
if ($a['name'] != $b['name']) {
    return $a['name'] < $b['name'] ? -1 : 1;
}
return 0;

Again, <=> makes this far more compact and readable.

Handling Mixed Data Types and Edge Cases

The spaceship operator follows PHP’s standard comparison rules (like in == vs ===), but it’s type-aware in a way that’s useful for sorting:

• Numbers are compared numerically.
• Strings are compared lexicographically.
• Integers and floats are handled correctly (e.g., 5 <=> 5.0 returns 0).

But be cautious with mixed types. For example:

echo 10 <=> "5 apples"; // Returns 1 (string "5 apples" becomes 5)

PHP uses loose comparison here, so type juggling may occur. If you need strict type handling, validate or cast your data before comparing.

Practical Tips for Using <=>

• Chain comparisons using arrays for multi-level sorting.
• Combine with null coalescing to handle missing keys:

  return [$a['age'] ?? 0, $a['name']] <=> [$b['age'] ?? 0, $b['name']];

• Use in class methods for implementing Comparable patterns:

  class Person {
      public function compare(self $other) {
          return [$this->age, $this->name] <=> [$other->age, $other->name];
      }
  }

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  Basically, the spaceship operator reduces boilerplate and makes sorting logic more intuitive. It doesn’t eliminate the need to understand comparison rules in PHP, but it does make expressing those rules a lot cleaner—especially when sorting by multiple criteria. Not magic, just smart syntax.

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