Notes

You can interact with other contracts by declaring an Interface. Interface:

• cannot have any functions implemented
• can inherit from other interfaces
• all declared functions must be external
• cannot declare a constructor
• cannot declare state variables

Code

solidity
Interface.sol
Copy
// 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);
   }
}