Data Location Assignment

samm8 · September 13, 2021, 4:31pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;
    
    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
        
        User storage user = users[id];
        user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

AthenaBelisle · September 13, 2021, 10:53pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
   users[id].balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

Esteban · September 14, 2021, 12:36am

Hi, I don’t want people getting rich easily


pragma solidity 0.7.5;

contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }
    
    modifier maxBalance(uint balance) {
        require(balance < 1000, "The balance should be less than 1000");
        _;
    }

    function addUser(uint id, uint balance) public maxBalance(balance) {
        users[id] = User(id, balance);
    }
    
    function updateBalance(uint id, uint balance) public maxBalance(balance)  {
         users[id].balance = balance;
    }

    
    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Also, we can play with adding a function addBalance to increment the existing balance. I can’t wait to learn SafeMath soon

alejandravisa · September 17, 2021, 10:29am

It took me time to find that the solution was in storage or memory. At the beginning I though that was necessary a constructor then I realized that it wasn’t. Then, I kept looking for any error in the code, variables or visibility and there I saw that the updateBalance function had to be saved permanently so that it updates the value that was given to the struct and that also, there could be two options to overwrite the balance or increase the existing balance with the new value.

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

        struct User{
            
            uint id;
            uint balance;
        }


    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }
    
    function updateBalance(uint id, uint balance) public {
        
         User storage user = users[id];
         user.balance += balance;
         
    }
    
    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

MatthiasTay · September 18, 2021, 2:51pm

Just change memory to storage, under the function updateBalance

problock101sjk · September 19, 2021, 4:26pm

// SPDX-License-Identifier: 3.0

pragma solidity 0.8.7;

contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

problock101sjk · September 19, 2021, 4:30pm

right. nice bro. Keep Going

CryptoKnight84 · September 22, 2021, 6:29pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         //User memory user = users[id];
         users[id].balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Apparently someone was trying to change permanent data in a local variable. How silly.

julcasans · September 22, 2021, 6:49pm

I’ve just replaced memory by storage and use a new variable as a ‘pointer’ to the internal variable users (although it isn’t necessary)

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage _user = users[id];
         _user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Divesh · September 23, 2021, 5:29am

In the updateBalance function we need to change the ‘memory’ to ‘storage’.

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Leonard_Gohlke · September 23, 2021, 5:49am

pragma solidity 0.7.5;

contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
     User storage user = users[id];
     user.balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

simfin94 · September 23, 2021, 6:42pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
     User storage user = users[id];
     user.balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

gaio · September 26, 2021, 5:11am

Here is my solution:

I replaced this:

User memory user = users[id];
user.balance = balance;

With this:

users[id].balance = balance;

^ this removed the short term memory of the user reference, and instead wrote the new balance directly to the user already in persistent storage. And this also consolidated into one less line of code.

Full revised code:


pragma solidity 0.7.5;
// SPDX-License-Identifier: UNLICENSED
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         users[id].balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

chen · September 30, 2021, 2:30pm

 mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

vale_dinap · September 30, 2021, 3:26pm

Just replaced the body of the function “updateBalance” with the line:
users[id].balance = balance;

Original code:

    function updateBalance(uint id, uint balance) public {
         User memory user = users[id];
         user.balance = balance;
    }

New code:

    function updateBalance(uint id, uint balance) public {
         users[id].balance = balance;
    }

moragarcia75 · October 1, 2021, 1:19pm

Used solidity 0.8.9 because it is the latest version. Did not get any errors.

pragma solidity 0.8.9;
contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
     users[id].balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

saishet · October 1, 2021, 7:14pm

pragma solidity 0.7.5;
contract MemoryAndStorage {
    mapping(uint => User) users;
    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }
}

dmatch · October 4, 2021, 6:32pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
     User (memory change to storage) user = users[id];
     user.balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

Aiden_Calhoun · October 4, 2021, 9:14pm

Memory and Storage
I updated memory to storage.

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

kylecullen · October 5, 2021, 10:38am

With the updateBalance function, the user cannot be local to the function as it relates to a state variable users[id]. Therefore set memory to storage.


pragma solidity 0.7.5;
contract MemoryAndStorage {
    
    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }
    
    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }
    
    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }
    
    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }
    
}