Example
PHP 7 introduces a new kind of operator, which can be used to compare expressions. This operator will return -1, 0 or 1 if the first expression is less than, equal to, or greater than the second expression.
// Integers
print (1 <=> 1); // 0
print (1 <=> 2); // -1
print (2 <=> 1); // 1
// Floats
print (1.5 <=> 1.5); // 0
print (1.5 <=> 2.5); // -1
print (2.5 <=> 1.5); // 1
// Strings
print ("a" <=> "a"); // 0
print ("a" <=> "b"); // -1
print ("b" <=> "a"); // 1
Objects are not comparable, and so doing so will result in undefined behaviour.
This operator is particularly useful when writing a user-defined comparison function using usort, uasort, or uksort. Given an array of objects to be sorted by their weight property, for example, an anonymous function can use <=> to return the value expected by the sorting functions.
usort($list, function($a, $b) { return $a->weight <=> $b->weight; });
In PHP 5 this would have required a rather more elaborate expression.
usort($list, function($a, $b) {
return $a->weight < $b->weight ? -1 : ($a->weight == $b->weight ? 0 : 1);
});
