为什么将现有的实体合同实例作为参数传递给合同构造函数

如何解决为什么将现有的实体合同实例作为参数传递给合同构造函数

对于https://ethereumdev.io/interact-with-other-contracts-from-solidity/中的以下代码段

contract CounterFactory {
 
    mapping(address => Counter) _counters;

    function createCounter() public {
        require (_counters[msg.sender] == Counter(0));
        _counters[msg.sender] = new Counter(msg.sender);
    }
    
    function increment() public {
        require (_counters[msg.sender] != Counter(0));
        Counter(_counters[msg.sender]).increment(msg.sender);
        // The following line also works as usual.
        // _counters[msg.sender].increment(msg.sender);
    }
    
    function getCount(address account) public view returns (uint256) {
        require (_counters[account] != Counter(0));
        return (_counters[account].getCount());
    }
    
    function getMyCount() public view returns (uint256) {
        return (getCount(msg.sender));
    }
 
}

为什么这一行（将constact实例传递给构造函数）起作用？ Counter(_counters[msg.sender]).increment(msg.sender);

我正在https://remix.ethereum.org/上使用Remix IDE