PHP - Spaceship Operator

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The Spaceship operator is one of the many new features introduced in PHP with its 7.0 version. It is a three-way comparison operator.

The conventional comparison operators (<, >, !=, ==, etc.) return true or false (equivalent to 1 or 0). On the other hand, the spaceship operator has three possible return values: -1,0,or 1. This operator can be used with integers, floats, strings, arrays, objects, etc.

Syntax of the Spaceship Operator

The symbol used for spaceship operator is "<=>".

$retval = operand1 <=> operand2

Here, $retval is -1 if operand1 is less than operand2, 0 if both the operands are equal, and 1 if operand1 is greater than operand2.

The spaceship operator is implemented as a combined comparison operator. Conventional comparison operators could be considered mere shorthands for <=> as the following table shows −

Example 1

The following example shows how you can use the spaceship operator in PHP. We will compare 5 with 10/2. As both values are equal so the result will be 0 −

<?php
   $x = 5;
   $y = 10;
   $z = $x <=> $y/2;

   echo "$x <=> $y/2 = $z";
?>

Output

It will create the following output −

5 <=> 10/2 = 0

Example 2

Now we change $x=4 and check the result. As 4 is less than 10/2 so the spaceship operator will return -1 −

<?php
   $x = 4;
   $y = 10;
   $z = $x <=> $y/2;

   echo "$x <=> $y/2 = $z";
?>

Output

It will produce the following output −

4 <=> 10/2 = -1

Example 3

Now let us change $y=7 and check the result again. Now 7 is greater than 10/2 so the spaceship operator will return 1 −

<?php
   $x = 7;
   $y = 10;
   $z = $x <=> $y/2;

   echo "$x <=> $y/2 = $z";
?>

Output

It will produce the following result −

7 <=> 10/2 = 1

Example 4

The spaceship operator, like the strcmp() method, works on strings. In this program, we will compare the phrases "bat" and "ball". Since "bat" comes after "ball" in alphabetical order so the result is 1.

<?php
   $x = "bat";
   $y = "ball";
   $z = $x <=> $y;

   echo "$x <=> $y = $z";
?>

Output

It will generate the following outcome −

bat <=> ball = 1

Example 5

Change $y = "baz" and check the result −

<?php
   $x = "bat";
   $y = "baz";
   $z = $x <=> $y;

   echo "$x <=> $y = $z";
?>

Output

It will produce the below output −

bat <=> baz = -1

Spaceship Operator with Boolean Operands

The spaceship operator also works with Boolean operands −

true <=> false returns 1
false <=> true returns -1
true <=> true as well as false <=> false returns 0