區塊鏈：元組 (Tuples)

什麼是元組

普通的數組返回方式

pragma solidity ^0.4.4;

contract C{

   uint[] data = [1,2,3,4,5];
   function f() constant returns (uint[]){
       return data;
   }
}

普通的字典返回value值方式，但是如何返回一個字典樣式的數據呢？

pragma solidity ^0.4.4;

contract C{

   mapping (uint => string) public students;
   function C(){
       students[0] = "wt";
       students[1] = "wtTwelveRngs";
   }

   function students(uint id) constant returns (string){
       return students[id];
   }
}

使用元組的方式

pragma solidity ^0.4.4;

contract C{

   mapping (uint => string) students;
   function C(){
       students[0] = "wt";
       students[1] = "wtTwelveRngs";
   }

   function students1() constant returns (string name0,string name1){
       name0 = students[0];
       name1 = students[1];
   }
   //students1等價於students2
   function students2() constant returns (string name0,string name1){
       name0 = students[0];
       name1 = students[1];

       return (name0,name1);
   }

   //元組，直接返回多種數據類型
   function f() constant returns (uint,bool,string){

       return (101,true,"wt");
   }
}

元組的使用

在聲明方法時，如果寫了確定的返回值時，可以省略return

pragma solidity ^0.4.4;

contract Simple{

   function arithmentics(uint _a,uint _b)constant returns(uint,uint){
       return (_a +_b,_a*_b);
   }

   function arithmentics1(uint _a,uint _b)constant returns(uint o_sum,uint o_product){
       o_sum = _a + _b;
       o_product = _a + _b;
   }
}

pragma solidity ^0.4.4;

contract Simple{

   function f() constant returns(uint,bool,uint){
       return(7,true,2);
   }

   function g1() constant returns(uint,bool,uint){
       var (x,b,y) = f();
       return(x,b,y);
   }

   function g2() constant returns(uint,uint){
       var (x,b,y) = f();
       (x,y) = (2,7);
       return (x,y);
   }
}