该<=>（“飞船”），运营商将提供，它会合并比较：

Return 0 if values on either side are equal
Return 1 if the value on the left is greater
Return -1 if the value on the right is greater

组合比较运算符使用的规则与PHP
viz当前使用的比较运算符相同。<，<=，==，>=和>。那些来自Perl或Ruby编程背景的人可能已经熟悉为PHP7建议的这个新运算符。

   //Comparing Integers

    echo 1 <=> 1; //output  0
    echo 3 <=> 4; //output -1
    echo 4 <=> 3; //output  1

    //String Comparison

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