21.Interface

可以通过声明接口来与其他合约进行交互。

Interface：

• 不能有任何实现的函数
• 可以继承其他接口
• 所有声明的函数必须是external
• 不能声明构造函数
• 不能声明state varibale

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

interface ICounter {
    function count() external view returns (uint);

    function increment() external;
}

contract Counter is ICounter{
    uint public mycount = 0;

    function count() external view returns (uint){
        return mycount;
    }

    function increment() external{
        mycount++;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Counter {
    uint public count;

    function increment() external {
        count += 1;
    }
}

interface ICounter {
    function count() external view returns (uint);

    function increment() external;
}

contract MyContract {
    function incrementCounter(address _counter) external {
        ICounter(_counter).increment();
    }

    function getCount(address _counter) external view returns (uint) {
        return ICounter(_counter).count();
    }
}

// Uniswap example
interface UniswapV2Factory {
    function getPair(
        address tokenA,
        address tokenB
    ) external view returns (address pair);
}

interface UniswapV2Pair {
    function getReserves()
        external
        view
        returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
}

contract UniswapExample {
    address private factory = 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f;
    address private dai = 0x6B175474E89094C44Da98b954EedeAC495271d0F;
    address private weth = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;

    function getTokenReserves() external view returns (uint, uint) {
        address pair = UniswapV2Factory(factory).getPair(dai, weth);
        (uint reserve0, uint reserve1, ) = UniswapV2Pair(pair).getReserves();
        return (reserve0, reserve1);
    }
}