双宾语可以互换位置，宾补可以吗

You can sing him a song.
And you can sing a song to/for him.
But that is different.
Just like I can spare you your life,
But you can not really turn it another way around.

在两个名词之间加上系动词 be（第一个名词如果是宾格代词则改成主格），如果成立就是宾宾补，不成立就是双宾。
例：
I bought my son a toy bear. 我儿子显然不是玩具熊，所以 My son is a toy bear 不成立，所以是双宾。
Classmates elected Xiaoming our monitor. 既然已经选了小明当班长，那现在小明当然就是班长，所以 Xiaoming is our monitor 成立，所以是宾宾补。

另外，双宾可以通过加介词把间宾改造成状语，从而变双宾为单宾。宾宾补则不能。
I bought my son a toy bear = I bought a toy bear for my son
Can you borrow me your ruler = Can you borrow your ruler to me
但 Classmates elected Xiaoming our monitor 不能改造成 Classmates elected our monitor to/for Xiaoming。