ActionChoices就是一个自定义的整型，当枚举数不够多时，它默认的类型为uint8，当枚举数足够多时，它会自动变成uint16。
pragma solidity ^0.4.4;
contract test {
enum ActionChoices { GoLeft, GoRight, GoStraight, SitStill }
ActionChoices _choice;
ActionChoices constant defaultChoice = ActionChoices.GoStraight;
function setGoStraight(ActionChoices choice) public {
_choice = choice;
}
function getChoice() constant public returns (ActionChoices) {
return _choice;
}
function getDefaultChoice() pure public returns (uint) {
return uint(defaultChoice);
}
}
上面的GoLeft == 0,GoRight == 1, GoStraight == 2, SitStill == 3。在setGoStraight方法中，我们传入的参数的值可以是0 - 3当传入的值超出这个范围时，就会中断报错。
invalid opcode
The execution might have thrown.
Debug the transaction to get more information
