Solidity Looping

syntax

supporting for and while loop，which syntax is similar to javascript language

core risk

looping may cause high-cost gas usage.

security warning

Never iterate over a dynamic storage array, since its length is unpredictable and can grow indefinitely.

Best practice

use mapping to instead of loop, because Mapping lookups always cost a fixed amount of gas.

❌ bad：as users grow, gas fee will grow indefinitely
address[] public users;
function isUser(address _user) public view returns (bool) {
    for (uint i = 0; i < users.length; i++) {
        if (users[i] == _user) {
            return true;
        }
    }
    return false;
}

✅ good
mapping(address => bool) public isUserMapping;
function isUserEfficient(address _user) public view returns (bool) {
    return isUserMapping[_user];
}