DeFi · hard

43. Flash loan provider

Lend within a single tx.

Given `interface IBorrower { function onFlashLoan(uint256 amt, uint256 fee) external; }`, implement `flashLoan(IBorrower b, uint256 amt)` that transfers ether, calls back, then requires the contract balance has grown by `fee` (1% of `amt`).

Required in your answer: address(b).call{value: amt}b.onFlashLoan(amt, fee)address(this).balance >= before + fee

Compiles with solc in your browser

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

interface IBorrower { function onFlashLoan(uint256 amt, uint256 fee) external; }
contract Pool {
    receive() external payable {}
    function flashLoan(IBorrower b, uint256 amt) external {
        uint256 before = address(this).balance;
        uint256 fee = amt / 100;
        // TODO transfer amt, call b.onFlashLoan, require repaid
    }
}

Output appears here.

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