请教一个 leetcode 上 Swift 语法展开问题

/** * Definition for singly-linked list. * public class ListNode { * public var val: Int * public var next: ListNode? * public init(_ val: Int) { * self.val = val * self.next = nil * } * } */ class Solution { func reverseList(_ head: ListNode?) -> ListNode? { var rev: ListNode? = nil, head = head while head != nil { (head, rev, head!.next) = (head!.next, head, rev) //请问下这段展开表达式 } return rev } } 

请问下如上标记那段的展开表达式是什么？