php7新增的两个操作符---null合并及飞船操作符

<?php
//null合并操作符??
//(太空)飞船操作符<=>
//The operator returns 0 if both operands are equal, 1 if the left is greater, and -1 if the right is greater.

$role = isset($_GET['role']) ? $_GET['role'] : 'guest';
echo $role;
echo '<br/>';

$user = $_GET['user'] ?? 'Anymous';
echo $user;
echo '<br/>';

echo 1.5 <=> 1.5;
echo '<br/>';
echo 1.5 <=> 2.5;
echo '<br/>';
echo 2.5 <=> 1.5;
echo '<br/>';
?>

输出

guest
Anymous
0
-1
1