PHP Spaceship Operator Explained

This article provides a clear overview of the PHP spaceship operator (<=>), which was introduced in PHP 7. You will learn how this three-way comparison operator works, what values it returns, and how to use it to write cleaner, more efficient sorting logic in your PHP applications.

The spaceship operator (<=>) is used to compare two expressions. Instead of returning a simple true or false boolean value, it returns one of three integers based on the outcome of the comparison: -1, 0, or 1.

How It Works

The operator compares the left-hand operand (\(a) to the right-hand operand (\)b) and behaves as follows:

• Returns 0 if $a is equal to \(b (\)a == $b)
• Returns -1 if $a is less than \(b (\)a < $b)
• Returns 1 if $a is greater than \(b (\)a > $b)

Here is a basic code example demonstrating these three outcomes:

// Integers
echo 1 <=> 1; // Outputs: 0  (1 is equal to 1)
echo 1 <=> 2; // Outputs: -1 (1 is less than 2)
echo 2 <=> 1; // Outputs: 1  (2 is greater than 1)

// Strings (compared alphabetically)
echo "a" <=> "a"; // Outputs: 0
echo "a" <=> "b"; // Outputs: -1
echo "b" <=> "a"; // Outputs: 1

Practical Use Case: Custom Sorting

The primary benefit of the spaceship operator is in sorting functions like usort(), uasort(), or uksort(). These functions require a callback that returns -1, 0, or 1 to determine the order of elements.

Before PHP 7, sorting required a verbose conditional statement:

// The old way
usort($array, function($a, $b) {
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
});

With the spaceship operator, this entire logic can be condensed into a single line:

// The modern way
usort($array, function($a, $b) {
    return $a <=> $b;
});

This operator works with integers, floats, strings, arrays, and objects, making it a highly versatile tool for data comparison in PHP.