『0019』 - Solidity Types - Solidity 字典／映射（Mappings）

2017-10-11 | 阅读：次

孔壹学院：国内区块链职业教育领先品牌

作者：黎跃春，区块链、高可用架构工程师微信：liyc1215 QQ群：348924182 博客：http://liyuechun.org

语法

mapping(_KeyType => _ValueType)

字典／映射其实就是一个一对一键值存储关系。

举个例子：

{age: 28, height: 172, name: liyuechun, wx: liyc1215}

这就是一个映射，满足_KeyType => _ValueType之间的映射关系，age对应一个28的值，height对应160，name对应liyuechun, wx对应liyc1215。

PS：同一个映射中，可以有多个相同的值，但是键必须具备唯一性。

案例

pragma solidity ^0.4.4;

contract MappingExample {
    
    // 测试账号
    
    // 0xca35b7d915458ef540ade6068dfe2f44e8fa733c
    
    // 0x14723a09acff6d2a60dcdf7aa4aff308fddc160c
    
    // 0x4b0897b0513fdc7c541b6d9d7e929c4e5364d2db
    
    mapping(address => uint)  balances;

    function update(address a,uint newBalance) public {
        balances[a] = newBalance;
    }
    
    // {0xca35b7d915458ef540ade6068dfe2f44e8fa733c: 100,0x14723a09acff6d2a60dcdf7aa4aff308fddc160c: 200,0x4b0897b0513fdc7c541b6d9d7e929c4e5364d2db: 300 }
    
    function searchBalance(address a) constant public returns (uint) {
        
        return balances[a];
    }
}

结构体和字典综合案例

pragma solidity ^0.4.4;

contract CrowdFunding {
    // Defines a new type with two fields.
    struct Funder {
        address addr;
        uint amount;
    }

    struct Campaign {
        address beneficiary;
        uint fundingGoal;
        uint numFunders;
        uint amount;
        mapping (uint => Funder) funders;
    }

    uint numCampaigns;
    mapping (uint => Campaign) campaigns;

    function newCampaign(address beneficiary, uint goal) public returns (uint campaignID) {
        campaignID = numCampaigns++; // campaignID is return variable
        // Creates new struct and saves in storage. We leave out the mapping type.
        campaigns[campaignID] = Campaign(beneficiary, goal, 0, 0);
    }

    function contribute(uint campaignID) public payable {
        Campaign storage c = campaigns[campaignID];
        // Creates a new temporary memory struct, initialised with the given values
        // and copies it over to storage.
        // Note that you can also use Funder(msg.sender, msg.value) to initialise.
        c.funders[c.numFunders++] = Funder({addr: msg.sender, amount: msg.value});
        c.amount += msg.value;
    }

    function checkGoalReached(uint campaignID) public returns (bool reached) {
        Campaign storage c = campaigns[campaignID];
        if (c.amount < c.fundingGoal)
            return false;
        uint amount = c.amount;
        c.amount = 0;
        c.beneficiary.transfer(amount);
        return true;
    }
}