pragma solidity ^0.4.16;
/**
 * The SpecialVariables contract does this and that...
 1.在属性定义的时候可以初始化，也可以调用全局变量，但是不能调用系统函数，
 2.在构造函数里可以调用系统函数。
 3.如果只是变动性为view的函数，无法改变参数，payable才有操作数，表示合约可支付
 */
contract SpecialVariables {
    uint public blockNum =  block.number;
    address public bolckCoin = block.coinbase;
    uint public minerDif = block.difficulty;
    uint public blockGaslimit = block.gaslimit;
    bytes32 public blockHash ;
    uint public blockTime = block.timestamp;
    uint256 public gasLeft ;
    address public addr = msg.sender;
    bytes4 public msgSig = msg.sig;
    uint public msgValue = msg.value;
    uint public Now = now;
    uint public gasPrice = tx.gasprice;
    address public txOrigin = tx.origin;
    uint[] public array = [1,2,3];
    byte public arr = byte(3);

    function SpecialVariables () public {
        blockHash =  block.blockhash(blockNum) ;
    }  
    function getBlockHash(uint _u) public payable returns(bytes32) {
        blockHash = block.blockhash(_u);
        return blockHash;
    }
}