Solidity - 函数修饰符

函数修饰符用于修改函数的Behave。例如，为函数添加先决条件。

首先我们创建一个带或不带参数的修饰符。

contract Owner {
   modifier onlyOwner {
      require(msg.sender == owner);
      _;
   }
   modifier costs(uint price) {
      if (msg.value >= price) {
         _;
      }
   }
}

函数体插入特殊符号“_;”的位置 出现在修饰符的定义中。因此，如果调用该函数时满足修饰符的条件，则执行该函数，否则将引发异常。

请参阅下面的示例 -

pragma solidity ^0.5.0;

contract Owner {
   address owner;
   constructor() public {
      owner = msg.sender;
   }
   modifier onlyOwner {
      require(msg.sender == owner);
      _;
   }
   modifier costs(uint price) {
      if (msg.value >= price) {
         _;
      }
   }
}
contract Register is Owner {
   mapping (address => bool) registeredAddresses;
   uint price;
   constructor(uint initialPrice) public { price = initialPrice; }
   
   function register() public payable costs(price) {
      registeredAddresses[msg.sender] = true;
   }
   function changePrice(uint _price) public onlyOwner {
      price = _price;
   }
}