[区块链]基于以太坊的智能合约开发教程Solidity modifier

pragma solidity ^0.4.0;

contract modifierTest{
    address owner;
    
    uint public a;
    
    constructor(){
        owner = msg.sender;
    }
    
    modifier onlyOwner{
        // 判断合约的调用者是否等于合约的拥有者
        require(msg.sender == owner);
        _;
    }
    
    function test1(uint _a) onlyOwner{
        // 附加上了modifier，先执行修饰符函数中的语句
        a = _a;
    }
}

contract modifierTest1{
    uint level = 5;
    string public name;
    uint public DNA;
    
    // 增加代码的重用性和拓展性
    modifier controller(uint _level){
        require(level >= _level);
        _;
    }
    
    
    function changeName(string _name) controller(2){
        name = _name;
    }
    
    function changeDNA(uint _DNA) controller(4){
        DNA = _DNA;
    }
}



contract modifierTest2{
    
    uint public a;
    
    modifier change1(){
        a = 10;
        _;
        a = 20;
    }
    
    modifier change2(){
        a = 30;
        _;
        a = 40;
    }
    // 当有两个修饰符函数时，先执行change1中的a=10；然后进入到change2当中的a=30;
    // 再进入到自己的函数体内a=100;再执行a=40;然后回到change1当中执行a=20  最后a的值为20
    function test() change1 change2{
        a = 100;
    }
}