gas costs and a small gotcha about address to bool mappings

solidity.mapping.BoolvsInt.sol

// SPDX-License-Identifier: MIT

pragma solidity 0.8.11;

contract MappingBool {
    
    // NB: if you need to distinguish from nil vs false this method does not work
    mapping(address => bool) entries;

    // gas 44463
    function add(address _a, bool _b) public {
        entries[_a] = _b;
    }
    
    // gas 24355
    function isTrue(address _a) public view returns (bool) {
        return entries[_a] == true;
    }

    // gas 24311
    // NB: this will return true for nil entries as well
    function isFalse(address _a) public view returns (bool) {
        return entries[_a] == false;
    }

}

contract MappingInt {
    
    // NB: if you need to specificall distinguish from nil vs false this method does not work
    mapping(address => uint256) entries;

    // gas 44452
    function add(address _a, bool _b) public {
        entries[_a] = _b == true ? 1 : 2;
    }
    // gas 24329
    function isTrue(address _a) public view returns (bool) {
        return entries[_a] == 1;
    }
    // gas 24263
    function isFalse(address _a) public view returns (bool) {
        return entries[_a] == 2;
    }

    // gas 24307
    function isSet(address _a) public view returns (bool) {
        return entries[_a] > 0;
    }
}