智能合約設(shè)計模式--COP

shadowbook 發(fā)布于2019-06-27 18:36 / 2432人閱讀

摘要：這樣的模式規(guī)范能保證合約的安全。函數(shù)主體沒有條件判斷例子改進后的風格擴展閱讀

Design by contract

solidity這門語言設(shè)計思路是什么？
什么是COP？

COP

面向條件的編程（COP）是面向合約編程的一個子域，作為一種面向函數(shù)和命令式編程的混合模式。COP解決了這個問題，通過需要程序員顯示地枚舉所有的條件。邏輯變得扁平，沒有條件的狀態(tài)變化。條件片段可以被正確的文檔化，復(fù)用，可以根據(jù)需求和實現(xiàn)來推斷。重要的是，COP在編程中把預(yù)先條件當作為一等公民。這樣的模式規(guī)范能保證合約的安全。

post-condition

contract PostCheck {

    uint public data = 0;

    // Check that the "data" field was set to the value of "_data".
    modifier data_is_valid(uint _data) {
        _
        if (_data != data)
            throw;
    }

    function setData(uint _data) data_is_valid(_data) {
        data = _data;
    }

}

pre- and post-conditions

"_"

contract PrePostCheck {

    uint public data = 0;

    // Check that the input "_data" value is not the same as the value
    // already stored in "data".
    modifier data_is_valid(uint _data) {
        if (_data == data)
           throw;
        _
    }

    // Check that the "data" field was set to the value of "_data".
    modifier data_was_updated(uint _data) {
        _
        if (_data != data)
            throw;
    }

    function setData(uint _data) data_is_valid(_data) data_was_updated(_data) {
        data = _data;
    }

}

FEATURES

函數(shù)主體沒有條件判斷

例子：

contract Token {
    // The balance of everyone
    mapping (address => uint) public balances;
    // Constructor - we"re a millionaire!
    function Token() {
        balances[msg.sender] = 1000000;
    }
    // Transfer `_amount` tokens of ours to `_dest`.
    function transfer(uint _amount, address _dest) {
        balances[msg.sender] -= _amount;
        balances[_dest] += _amount;
    }
}

改進后：

function transfer(uint _amount, address _dest) {
    if (balances[msg.sender] < _amount)
        return;
    balances[msg.sender] -= _amount;
    balances[_dest] += _amount;
}

COP的風格

modifier only_with_at_least(uint x) {
    if (balances[msg.sender] >= x) _;
}

function transfer(uint _amount, address _dest)
only_with_at_least(_amount) {
    balances[msg.sender] -= _amount;
    balances[_dest] += _amount;
}

擴展閱讀：

Condition-Orientated Programming