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| pragma solidity ^0.4.2; | |
| library Set { | |
| // library 不能真的有狀態變數，但呼叫 library 的合約可以擁有 (請見下方 contract) | |
| struct Data { mapping(uint => bool) flags; } | |
| // 加上 storage 修飾字之後，self 就會指向呼叫 library 的合約的某個狀態變數 | |
| // 此為 library 特有的功能 | |
| function insert(Data storage self, uint value) returns (bool) { | |
| if (self.flags[value]) | |
| return false; // value already there | |
| self.flags[value] = true; | |
| return true; | |
| } | |
| function remove(Data storage self, uint value) returns (bool) { | |
| if (!self.flags[value]) | |
| return false; // not there | |
| self.flags[value] = false; | |
| return true; | |
| } | |
| function contains(Data storage self, uint value) returns (bool) { | |
| return self.flags[value]; | |
| } | |
| } | |
| contract C { | |
| // 建立 library 裡面需要的實體個體 Data (Data 在這是一個變數) | |
| Set.Data knownValues; | |
| function register(uint value) { | |
| // 呼叫 library 中的方法 | |
| // 假如今天 library 裡面有 this，那麼就是指 C 這個合約 | |
| if (!Set.insert(knownValues, value)) | |
| throw; | |
| } | |
| // 我們也可以直接 knownValues.flags 來存取實體 Data 結構中的 flags | |
| } |
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