智能合約函數(shù)通過ABI(Application Binary Interface，應(yīng)用二進(jìn)制接口)和外部業(yè)務(wù)系統(tǒng)交互，ABI往往通過JSON文件表示，ABI文件是智能合約編譯后的產(chǎn)物。

　　區(qū)塊鏈存儲的智能合約都是二進(jìn)制格式的，When the virtual machine executes these binary files,there needs to be a suitable way to pass on which smart contract function is called by the external system,并傳遞哪些參數(shù)，通過對ABI中的JSON數(shù)據(jù)解析就可以得出這些信息。

　　這里將ABI和API進(jìn)行對比：API是程序間交互的接口，接口包含程序提供外界存取所需的函數(shù)、參數(shù)等內(nèi)容；ABI也是程序間交互的接口，但程序是被編譯后的二進(jìn)制字節(jié)碼，傳遞的是二進(jìn)制格式的信息，ABI用于描述如何編解碼程序間傳遞的二進(jìn)制信息。

//this low-level function should be called from a contract which performs important safety checks

　　function mint(address to)external lock returns(uint liquidity){

　　(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings

　　uint balance0=IERC20(token0).balanceOf(address(this));

　　uint balance1=IERC20(token1).balanceOf(address(this));

　　uint amount0=balance0.sub(_reserve0);

　　uint amount1=balance1.sub(_reserve1);

　　bool feeOn=_mintFee(_reserve0,_reserve1);

　　uint _totalSupply=totalSupply;//gas savings,must be defined here since totalSupply can update in _mintFee

　　if(_totalSupply==0){

　　liquidity=Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);

　　_mint(address(0),MINIMUM_LIQUIDITY);//permanently lock the first MINIMUM_LIQUIDITY tokens

　　}else{

　　liquidity=Math.min(amount0.mul(_totalSupply)/_reserve0,amount1.mul(_totalSupply)/_reserve1);

　　}

　　require(liquidity>0,'UniswapV2:INSUFFICIENT_LIQUIDITY_MINTED');

　　_mint(to,liquidity);

　　_update(balance0,balance1,_reserve0,_reserve1);

　　if(feeOn)kLast=uint(reserve0).mul(reserve1);//reserve0 and reserve1 are up-to-date

　　emit Mint(msg.sender,amount0,amount1);

　　}

　　//this low-level function should be called from a contract which performs important safety checks

　　function burn(address to)external lock returns(uint amount0,uint amount1){

　　(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings

　　address _token0=token0;//gas savings

　　address _token1=token1;//gas savings

　　uint balance0=IERC20(_token0).balanceOf(address(this));

　　uint balance1=IERC20(_token1).balanceOf(address(this));

　　uint liquidity=balanceOf[address(this)];

　　bool feeOn=_mintFee(_reserve0,_reserve1);

　　uint _totalSupply=totalSupply;//gas savings,must be defined here since totalSupply can update in _mintFee

　　amount0=liquidity.mul(balance0)/_totalSupply;//using balances ensures pro-rata distribution

　　amount1=liquidity.mul(balance1)/_totalSupply;//using balances ensures pro-rata distribution

　　require(amount0>0&&amount1>0,'UniswapV2:INSUFFICIENT_LIQUIDITY_BURNED');

　　_burn(address(this),liquidity);

　　_safeTransfer(_token0,to,amount0);

　　_safeTransfer(_token1,to,amount1);

　　balance0=IERC20(_token0).balanceOf(address(this));

　　balance1=IERC20(_token1).balanceOf(address(this));

　　_update(balance0,balance1,_reserve0,_reserve1);

　　if(feeOn)kLast=uint(reserve0).mul(reserve1);//reserve0 and reserve1 are up-to-date

　　emit Burn(msg.sender,amount0,amount1,to);

　　}

　　//this low-level function should be called from a contract which performs important safety checks

　　function swap(uint amount0Out,uint amount1Out,address to,bytes calldata data)external lock{

　　require(amount0Out>0||amount1Out>0,'UniswapV2:INSUFFICIENT_OUTPUT_AMOUNT');

　　(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings

　　require(amount0Out<_reserve0&&amount1Out<_reserve1,'UniswapV2:INSUFFICIENT_LIQUIDITY');

　　uint balance0;

　　uint balance1;

　　{//scope for _token{0,1},avoids stack too deep errors

　　address _token0=token0;

　　address _token1=token1;

　　require(to!=_token0&&to!=_token1,'UniswapV2:INVALID_TO');

　　if(amount0Out>0)_safeTransfer(_token0,to,amount0Out);//optimistically transfer tokens

　　if(amount1Out>0)_safeTransfer(_token1,to,amount1Out);//optimistically transfer tokens

　　if(data.length>0)IUniswapV2Callee(to).uniswapV2Call(msg.sender,amount0Out,amount1Out,data);

　　balance0=IERC20(_token0).balanceOf(address(this));

　　balance1=IERC20(_token1).balanceOf(address(this));

　　}