Lesson 7: More optimized withdraw

[carledwardfp]

I tried a different gas optimization for the withdraw function containing for loop:

function withdraw() public onlyOwner {
    uint256 fundersLength = s_funders.length;

    for (uint256 i = 0; i < fundersLength; i++) {
        address funder = s_funders[i];
        s_funderToAmountFunded[funder] = 0;
    }
    s_funders = new address[](0);

    (bool success, ) = payable(i_owner).call{value: address(this).balance}("");
    if (!success) revert FundMe__CallFailed();
}

And it generated a better result as seen in gas-report.txt:

·-------------------------|----------------------------|-------------|-----------------------------·
|  Solc version: 0.8.17   ·  Optimizer enabled: false  ·  Runs: 200  ·  Block limit: 30000000 gas  │
··························|····························|·············|······························
|  Methods                                                                                         │
·············|············|·············|··············|·············|···············|··············
|  Contract  ·  Method    ·  Min        ·  Max         ·  Avg        ·  # calls      ·  usd (avg)  │
·············|············|·············|··············|·············|···············|··············
|  FundMe    ·  fund      ·      42703  ·      104181  ·      90513  ·           21  ·          -  │
·············|············|·············|··············|·············|···············|··············
|  FundMe    ·  withdraw  ·      35562  ·       69373  ·      45222  ·            7  ·          -  │
·············|············|·············|··············|·············|···············|··············
|  Deployments            ·                                          ·  % of limit   ·             │
··························|·············|··············|·············|···············|··············
|  FundMe                 ·          -  ·           -  ·     781080  ·        2.6 %  ·          -  │
··························|·············|··············|·············|···············|··············
|  MockV3Aggregator       ·          -  ·           -  ·     569611  ·        1.9 %  ·          -  │
·-------------------------|-------------|--------------|-------------|---------------|-------------·

As compared to:

function withdraw() public onlyOwner {
    address[] memory funders = s_funders;

    for (uint256 i = 0; i < funders.length; i++) {
        address funder = funders[i];
        s_funderToAmountFunded[funder] = 0;
    }
    s_funders = new address[](0);

    (bool success, ) = payable(i_owner).call{value: address(this).balance}("");
    if (!success) revert FundMe__CallFailed();
}

·-------------------------|----------------------------|-------------|-----------------------------·
|  Solc version: 0.8.17   ·  Optimizer enabled: false  ·  Runs: 200  ·  Block limit: 30000000 gas  │
··························|····························|·············|······························
|  Methods                                                                                         │
·············|············|·············|··············|·············|···············|··············
|  Contract  ·  Method    ·  Min        ·  Max         ·  Avg        ·  # calls      ·  usd (avg)  │
·············|············|·············|··············|·············|···············|··············
|  FundMe    ·  fund      ·      42703  ·      104181  ·      90513  ·           21  ·          -  │
·············|············|·············|··············|·············|···············|··············
|  FundMe    ·  withdraw  ·      35725  ·       69316  ·      45322  ·            7  ·          -  │
·············|············|·············|··············|·············|···············|··············
|  Deployments            ·                                          ·  % of limit   ·             │
··························|·············|··············|·············|···············|··············
|  FundMe                 ·          -  ·           -  ·     801619  ·        2.7 %  ·          -  │
··························|·············|··············|·············|···············|··············
|  MockV3Aggregator       ·          -  ·           -  ·     569611  ·        1.9 %  ·          -  │
·-------------------------|-------------|--------------|-------------|---------------|-------------·

Compiler used: 0.8.17

[carledwardfp]

This can further be optimized to

function withdraw() public onlyOwner {
    uint256 fundersLength = s_funders.length;

    for (uint256 i = 0; i < fundersLength; ) {
        address funder = s_funders[i];
        s_funderToAmountFunded[funder] = 0;
        unchecked {
            i++;
        }
    }
    s_funders = new address[](0);

    (bool success, ) = payable(i_owner).call{value: address(this).balance}("");
    if (!success) revert FundMe__CallFailed();
}

·-------------------------|----------------------------|-------------|-----------------------------·
|  Solc version: 0.8.17   ·  Optimizer enabled: false  ·  Runs: 200  ·  Block limit: 30000000 gas  │
··························|····························|·············|······························
|  Methods                                                                                         │
·············|············|·············|··············|·············|···············|··············
|  Contract  ·  Method    ·  Min        ·  Max         ·  Avg        ·  # calls      ·  usd (avg)  │
·············|············|·············|··············|·············|···············|··············
|  FundMe    ·  fund      ·      42703  ·      104181  ·      90513  ·           21  ·          -  │
·············|············|·············|··············|·············|···············|··············
|  FundMe    ·  withdraw  ·      35431  ·       68858  ·      44982  ·            7  ·          -  │
·············|············|·············|··············|·············|···············|··············
|  Deployments            ·                                          ·  % of limit   ·             │
··························|·············|··············|·············|···············|··············
|  FundMe                 ·          -  ·           -  ·     778260  ·        2.6 %  ·          -  │
··························|·············|··············|·············|···············|··············
|  MockV3Aggregator       ·          -  ·           -  ·     569611  ·        1.9 %  ·          -  │
·-------------------------|-------------|--------------|-------------|---------------|-------------·

since we are sure that we wont overflow or underflow [reference]