Uniswap v4 Core: Automated market maker protocol

import {IPoolManager} from 'v4-core/contracts/interfaces/IPoolManager.sol';
import {IUnlockCallback} from 'v4-core/contracts/interfaces/callback/IUnlockCallback.sol';

contract MyContract is IUnlockCallback {
    IPoolManager poolManager;

    function doSomethingWithPools() {
        // this function will call `unlockCallback` below
        poolManager.unlock(...);
    }

    function unlockCallback(bytes calldata data) external returns (bytes memory) {
        // disallow arbitrary caller
        if (msg.sender != address(poolManager)) revert Unauthorized();
        // perform pool actions
        poolManager.swap(...)
    }
}

error Unauthorized();