区块链学堂（23）：Enum数据类型-蒲公英云

区块链学堂（23）：Enum数据类型

Enums类型的官方定义

Enums are one way to create a user-defined type in Solidity. They are explicitly convertible to and from all integer types but implicit conversion is not allowed. The explicit conversions check the value ranges at runtime and a failure causes an exception. Enums needs at least one member.here

Enum类型定义

enum ActionCode {Left,Right, Forward, Rollback}
  ActionCode public b2;

Enum的Demo代码

Step 1: 首先定义enum类型

pragma solidity 0.4.7;
contract Demo {
```
enum ActionCode {Left,Right, Forward}
ActionCode public b2;
```
}
Step 2: 设置一个构造函数，并给变量b2赋予一个初始值
```
function Demo() {
      b2 = ActionCode.Left;
  }
```

Step 3：设置一个判断函数，输出结果

function f() returns (string str) {
      if (b2 == ActionCode.Left) return "Left";
  }

Step1-3的完整代码如下：

pragma solidity 0.4.10;
contract Demo {
    enum ActionCode {Left,Right, Forward}
    ActionCode public b2;
    function Demo() {
        b2 = ActionCode.Left;
    }
    function f() returns (string str) {
        if (b2 == ActionCode.Left) return "Left";
    }
}

Step 1-3，实现了enum（枚举）类型的功能，在构造函数中设置变量b2的初始值，然后根据b2的value来进行判断。

Step 4: 在Step1-3的基础上添加几个function。Left()/Right()/Forward()

function Left() {
      b2 = ActionCode.Left;
  }
  function Right() {
      b2 = ActionCode.Right;
  }
  function Forward() {
      b2 = ActionCode.Forward;
  }

Step 5: 修改f(), 增加两个输出

if (b2 == ActionCode.Right) return "Right";
      if (b2 == ActionCode.Forward) return "Forward";

完整代码如下：

pragma solidity 0.4.7;
contract Demo {
    enum ActionCode {Left,Right, Forward}
    ActionCode public b2;
    function Demo() {
        b2 = ActionCode.Left;
    }
    function Left() {
        b2 = ActionCode.Left;
    }
    function Right() {
        b2 = ActionCode.Right;
    }
    function Forward() {
        b2 = ActionCode.Forward;
    }
    function f() returns (string str) {
        if (b2 == ActionCode.Left) return "Left";
        if (b2 == ActionCode.Right) return "Right";
        if (b2 == ActionCode.Forward) return "Forward";
    }
}