> For the complete documentation index, see [llms.txt](https://chihaolu.gitbook.io/all-in-one-solidity/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://chihaolu.gitbook.io/all-in-one-solidity/part-i-basic/chapter-6-zi-liao-jie-gou-data-structures/enum.md).

# 【Enum】

枚舉（`enum`）和 `struct` 非常類似，只是 `enum` 中的每個參數會自動從 0 開始依序初始化。

Enum具有以下的性質：

* 內部已有整數型態的元素存在
* 可以存進uint8的型態，如果數值數量介於0\~255，若大於256個值則可宣告為uint16

```solidity
enum ActionChoices { GoLeft, GoRight, GoStraight, SitsStill }
ActionChoices choice;
ActionChoices constant defaultChoice = ActionChoices.Gostraight;
```

在 Solidity 中 `enum` 更常被用來進行模型選擇（model choice），或者追蹤狀態（track of state）。

```solidity
pragma solidity ^0.8.11;

contract MyEnums {
    
    enum Rarity {
        original, // 0
        rare, // 1
        super_rare // 2
    }
    
    Rarity public rarity;
    
    constructor() {
        rarity = Rarity.rare;
    }
    
    // 我們可以直接將一個型態為該 enum 的變數賦值為某特定屬性
    function makeSuperRare() public {
        rarity = Rarity.super_rare;
    }
    
    // 我們可以藉由 enum 初始化的 INDEX 來進行賦值
    function set(Rarity _rarity) public {
        rarity = _rarity;
    }
    
    // 我們可以藉由 delete 來重置這個 enum 成他的初始值 0
    function reset() public {
        delete rarity;
    }
}
```

`struct` 和 `enum` 的差別：

* Struct 用於表示一個複雜變數
* Enum 用於表示一個單一變數的不同狀態或值


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