什么是去中心化应用程序(DApp)以及它们如何工作？
您可能想知道是什么元素使DApp能够工作。可以通过将DApp分成不同的部分来提供最简单的解释：
DApps和传统应用程序有许多共同点。例如，两者都需要计算基础设施和编程语言来创建其操作所需的逻辑。DApps和传统应用程序之间最显着的区别从这里开始：
在DApp中，计算能力来自通常通过区块链或其他去中心化基础设施组织的去中心化节点网络。在应用程序中，计算能力通常来自我们的计算机（客户端应用程序）。或者来自服务器（服务器端应用程序），这表示高度集中。
Smart contract is a computer protocol designed to disseminate,verify or execute contracts in an information-based manner.It's a bit like a technology that everyone makes rules and the machine automatically executes them.Because the data stored and maintained in the network always needs to be executed by someone,and smart contracts can also conduct trusted transactions without a third party,
and these transactions can be tracked and irreversible.Therefore,smart contracts play a major role in data execution in the syste
pragma solidity=0.5.16;
import'./interfaces/IUniswapV2ERC20.sol';
import'./libraries/SafeMath.sol';
contract UniswapV2ERC20 is IUniswapV2ERC20{
using SafeMath for uint;
string public constant name='Uniswap V2';
string public constant symbol='UNI-V2';
uint8 public constant decimals=18;
uint public totalSupply;
mapping(address=>uint)public balanceOf;
mapping(address=>mapping(address=>uint))public allowance;
bytes32 public DOMAIN_SEPARATOR;
//keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
bytes32 public constant PERMIT_TYPEHASH=0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
mapping(address=>uint)public nonces;
event Approval(address indexed owner,address indexed spender,uint value);
event Transfer(address indexed from,address indexed to,uint value);
constructor()public{
uint chainId;
assembly{
chainId:=chainid
}
DOMAIN_SEPARATOR=keccak256(
abi.encode(
keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
keccak256(bytes(name)),
keccak256(bytes('1')),
chainId,
address(this)
)
);
}
function _mint(address to,uint value)internal{
totalSupply=totalSupply.add(value);
balanceOf[to]=balanceOf[to].add(value);
emit Transfer(address(0),to,value);
}
function _burn(address from,uint value)internal{
balanceOf[from]=balanceOf[from].sub(value);
totalSupply=totalSupply.sub(value);
emit Transfer(from,address(0),value);
}
function _approve(address owner,address spender,uint value)private{
allowanceowner=value;
emit Approval(owner,spender,value);
}
function _transfer(address from,address to,uint value)private{
balanceOf[from]=balanceOf[from].sub(value);
balanceOf[to]=balanceOf[to].add(value);
emit Transfer(from,to,value);
}
