<?php
This <=> operator will offer combined comparison in that it will :

Return 0 if values on either side are equal
Return 1 if value on the left is greater
Return -1 if the value on the right is greater
The rules used by the combined comparison operator are same as the currently used comparison operators by PHP viz. <, <=, ==, >= and >. Those who are from Perl or Ruby programming background may already be familiar with this new operator proposed for PHP7.

   //Comparing Integers

    echo 1 <=> 1; //ouputs 0
    echo 3 <=> 4; //outputs -1
    echo 4 <=> 3; //outputs 1

    //String Comparison

    echo "x" <=> "x"; // 0
    echo "x" <=> "y"; //-1
    echo "y" <=> "x"; //1