How does <=> in php 7 responsed in situations that check bool values? - php

Question

Looking into php 7 on the way, but <=> confuses me.
Most of the time I use conditional operators, they are used in boolean situations (which <=> almost is, but not quite, being able to return -1 as well). (If X <=> Y). So I'm not sure what will happen in the following cases...
if ($x <=> $y) {
// Do all the 1 things
} else {
// Do all the 2 things
}
What can I expect if it's preceded by...
$x = 0; $y = 1;
or
$x = "Carrot"; $y = "Carrot Juice";
or
$x = "Carrot Juice"; $y = "Carrot";
or
$x = array(carrot, juice); $y = "carrot juice";
There's definitely enough cases about this that it's confusing me as to what it'll do.

Answer 1

The spaceship operator (and other PHP 7 additions) is explained in plain language here:
https://blog.engineyard.com/2015/what-to-expect-php-7
It's mostly useful in the comparison function supplied to functions like usort.
// Pre PHP 7
function order_func($a, $b) {
return ($a < $b) ? -1 : (($a > $b) ? 1 : 0);
}
// Post PHP 7
function order_func($a, $b) {
return $a <=> $b;
}
It's not very useful in if, because if only checks whether the value is truthy or falsey, the different truthy values representing the ordering are not distinguished. If you do use it in a boolean context, it will be considered true when the values are different (because 1 and -1 are bother truthy), false when they're equal (because 0 is falsey). This is similar to trying to use strcmp() and stricmp() in a boolean context, which is why you often see
if (stricmp($x, $y) == 0)
The rules for using arrays with comparison operators is given here (scroll down to the table labeled Comparison with Various Types). When comparing an array with another array, the rule is:
Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are uncomparable, otherwise - compare value by value
When comparing an array with another type, the array is always greater. So array('carrot', 'juice') <=> 'carrot juice' will be 1.

Answer 2

Why not just try it out for yourself and play around with that new spaceship you got?
Demo
Also if you are wondering how the comparison of the spaceship operator works, see: http://php.net/manual/en/types.comparisons.php
But now if we want to go into a bit more detail about your test data:
First case:
//Test data
$x = 0;
$y = 1;
//operator
0 <=> 1 //0 is smaller than 1, so result: -1
//-1 evaluates to TRUE in the if statement
Second case:
//Test data
$x = "Carrot";
$y = "Carrot Juice";
//operator
"Carrot" <=> "Carrot Juice" //"Carrot" is smaller than "Carrot Juice", so result: -1
//-1 evaluates to TRUE in the if statement
Third case:
//Test data
$x = "Carrot Juice";
$y = "Carrot";
//operator
"Carrot Juice" <=> "Carrot" //"Carrot Juice" is bigger than "Carrot", so result: 1
//1 evaluates to TRUE in the if statement
Fourth case:
//Test data
$x = array("carrot", "juice");
$y = "carrot juice";
//operator
array("carrot", "juice") <=> "carrot juice" //array("carrot", "juice") is bigger than "carrot juice", so result: 1
//1 evaluates to TRUE in the if statement

Answer 3

Introduction
The spaceship operator <=> is a non-associative binary operator with the same precedence as equality operators (==, !=, ===, !==).
The purpost of this operator, is to allow for simpler three-way comparison between left-hand and right-hand operands.
Possible outcomes
The operator can produce any of the following results :
0 : when both operands are equal
-1 : when the left-hand operand is less than the right-hand operand
1 : when the left-hand operand is greater than the right-hand operand.
So, that means :
1 <=> 1; // output : 0
1 <=> 2; // output : -1
2 <=> 1; // output : 1
Practical application
A good practical application of using this operator would be in comparison type callbacks that are expected to return a zero, negative, or positive integer based on a three-way comparison between two values. The comparison function passed to usort is one such example.
Before PHP 7, you would write this :
$arr = [4,2,1,3];
usort($arr, function ($a, $b) {
if ($a < $b) {
return -1;
} elseif ($a > $b) {
return 1;
} else {
return 0;
}
});
Since PHP 7, you can write this :
$arr = [4,2,1,3];
usort($arr, function ($a, $b) {
return $a <=> $b;
});