多签钱包需要维护多个钱包所有者地址，满足一定数量的签名后，才可以发起交易。如果只用一个数组address[]去存储所有者地址，在检查某地址是否是所有者地址时需要遍历此数组，时间效率是O(n)。为了提高到O(1)，通常做法可以是增加一个mapping(address=>bool)来存储某地址是否是所有者地址，但这样下来增加了storage的操作。Gnosis safe用了一个哨兵mapping来存储，可以改善此问题。

address internal constant SENTINEL_OWNERS = address(0x1);
mapping(address => address) internal owners;

假设有A,B,C三个所有者地址，储存到owners后，变为

owners[address(0x1)] = A
owners[A] = B
owners[B] = C
owners[C] = address(0x1)

这样，要判断某地址是否属于所有者地址时，只需O(1)，且storage只用了一个mapping

function isOwner(address owner) public view returns (bool) {
        return owner != SENTINEL_OWNERS && owners[owner] != address(0);
    }

如果要增加一个D地址，则变为

owners[address(0x1)] = D
owners[D] = A
owners[A] = B
owners[B] = C
owners[C] = address(0x1)

时间效率也是O(1)，相应代码是（此处只列出动态链表相关操作的代码）

function addOwner(address owner){
  owners[owner] = owners[SENTINEL_OWNERS];
  owners[SENTINEL_OWNERS] = owner;
}

如果要删除B地址，则变为

owners[address(0x1)] = D
owners[D] = A
owners[A] = C
owners[C] = address(0x1)

时间效率也是O(1)，相应代码是（此处只列出动态链表相关操作的代码）

function removeOwner(address prevOwner,address owner){
  owners[prevOwner] = owners[owner];
  owners[owner] = address(0);
}//这里需要先在链下查到要删除地址的前一个地址，再直接传参数到链上去删除，节省链上计算gas

总体来说，这种数据结构还是很实用的，在gas cost上也很有帮助。

多签钱包需要维护多个钱包所有者地址，满足一定数量的签名后，才可以发起交易。如果只用一个数组address[]去存储所有者地址，在检查某地址是否是所有者地址时需要遍历此数组，时间效率是O(n)。为了提高到O(1)，通常做法可以是增加一个mapping(address=>bool)来存储某地址是否是所有者地址，但这样下来增加了storage的操作。Gnosis safe用了一个哨兵mapping来存储，可以改善此问题。

address internal constant SENTINEL_OWNERS = address(0x1);
mapping(address => address) internal owners;

假设有A,B,C三个所有者地址，储存到owners后，变为

owners[address(0x1)] = A
owners[A] = B
owners[B] = C
owners[C] = address(0x1)

这样，要判断某地址是否属于所有者地址时，只需O(1)，且storage只用了一个mapping

function isOwner(address owner) public view returns (bool) {
        return owner != SENTINEL_OWNERS && owners[owner] != address(0);
    }

如果要增加一个D地址，则变为

owners[address(0x1)] = D
owners[D] = A
owners[A] = B
owners[B] = C
owners[C] = address(0x1)

时间效率也是O(1)，相应代码是（此处只列出动态链表相关操作的代码）

function addOwner(address owner){
  owners[owner] = owners[SENTINEL_OWNERS];
  owners[SENTINEL_OWNERS] = owner;
}

如果要删除B地址，则变为

owners[address(0x1)] = D
owners[D] = A
owners[A] = C
owners[C] = address(0x1)

时间效率也是O(1)，相应代码是（此处只列出动态链表相关操作的代码）

function removeOwner(address prevOwner,address owner){
  owners[prevOwner] = owners[owner];
  owners[owner] = address(0);
}//这里需要先在链下查到要删除地址的前一个地址，再直接传参数到链上去删除，节省链上计算gas

总体来说，这种数据结构还是很实用的，在gas cost上也很有帮助。