[C++知识库]solidity中reference type

solidity中5种reference type:
1.struct
2.array
3.map
4.enum
5.string
sames首字母缩写

一.stuct
多维的结构，结构体内还可以再包含字符串，整型，映射，结构体等复杂类型

1.设置struct 名称A
struct A{
string title;
string author;
uint book_id;
}
2.声明变量一样，声明一个变量book，指定类型为刚刚设置的struct名字A
A book;
3.写入book = A(’’, ‘’, 1) //按照struct传参
// 第一种
book.push(A(titlename, ‘TP’, 1));
// 第二种
book.push(A({
title:titlename,
author: ‘dhk’,
book_id:2
}));
// 第三种
A memory mybook;
mybook.title = titlename;
mybook.author = ‘newauthor’;
mybook.book_id = 3;
book.push(mybook);

4.读取book.book_id

pragma solidity ^0.5.0;
contract test {
   struct A{
      string title;
      string author;
      uint book_id;
   }
   A book;
   function setBook() public {
      book = A('Learn Java', 'TP', 1);
   }
   function getBookId() public view returns (uint) {
      return book.book_id;
   }
}

二、数组[]
1.设置数组类型: uint [] name;
2.数组和struct结合

pragma solidity ^0.5.0;
contract test {
   struct A {
      string title;
      string author;
      uint book_id;
   }
   A[] public book; //定义数组book，里面类型是A
   function setBook(string memory titlename) public {
   // 第一种
      book.push(A(titlename, 'TP', 1)); 
    //   第二种
    book.push(A({
        title:titlename,
        author: 'dhk',
        book_id:2
    })); 
        // 第三种
    A memory mybook;
    mybook.title = titlename;
    mybook.author = 'newauthor';
    mybook.book_id = 3;
    book.push(mybook);
   }
   function getBookId() public view returns (string memory) {
      return book[1].author;
   }
}

三、mapping
mapping(key_type=> value_type) public A;
把struct放进map里面，一维对象放进多维对象。

pragma solidity ^0.5.0;
contract Store{

    struct Product{
        uint productId;
        uint productValue;
    }
    
    mapping (uint=>Product) products;
    
    function save() public {
        Product  memory product = Product(2,93);
        products[120]=product;
    }

    function getPriceOfProductId(uint productId) public view returns (uint){  
        return products[productId].productValue;
    }
}

四、enum
一维的
枚举类型，定好规则，到里面取。类型到咖啡厅，定好大中小杯。方便客户。

pragma solidity ^0.5.0;
contract Enumtest {
   enum FreshJuiceSize{ SMALL, MEDIUM, LARGE } // 对应的：0,1,2
   FreshJuiceSize choice;
   FreshJuiceSize constant defaultChoice = FreshJuiceSize.MEDIUM;
   function setLarge() public {
      choice = FreshJuiceSize.LARGE; // 返回2
   }
   function getChoice() public view returns (FreshJuiceSize) {
      return choice;
   }
   function getDefaultChoice() public pure returns (uint) {
      return uint(defaultChoice); // 返回1
   }
}

五、string
一维的
Solidity提供字节与字符串之间的内置转换，可以将字符串赋给 byte32类型变量。

pragma solidity ^0.5.0;
contract SolidityTest {
   string data = "test";
   bytes32 data2 = "test"; // 把string隐式转为bytes32
   function mydata() public pure {
       bytes memory bstr = new bytes(10);
       string memory message = string(bstr); // 显式转为string
   }
}