Design by contract

solidity这门语言设计思路是什么？

COP

面向条件的编程（COP）是面向合约编程的一个子域，作为一种面向函数和命令式编程的混合模式。COP解决了这个问题，通过需要程序员显示地枚举所有的条件。逻辑变得扁平，没有条件的状态变化。条件片段可以被正确的文档化，复用，可以根据需求和实现来推断。重要的是，COP在编程中把预先条件当作为一等公民。这样的模式规范能保证合约的安全。

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

• 函数主体没有条件判断

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;    }}

改进后：

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

COP的风格

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;}

扩展阅读：