Data Location Assignment

Daf72 · March 15, 2021, 9:05am

Changed memory with 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;
}

Toddness · March 15, 2021, 3:23pm

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;**

** /the Struct is in “Storage”. So we can delete “memory” here and just update the Struct by updating the index by pushing the new balance/ **

}

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

}

Nissa · March 15, 2021, 3:33pm

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;
}

}

KryptoS · March 16, 2021, 9:35am

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; //update
    }

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

}

Mariano_Collarte · March 16, 2021, 6:58pm

Update the updateBalance function to the following:

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

karips · March 17, 2021, 7:37am

Balance is not updated in the state variable that users. A straightforward solution is to replace the user entry with a new User instance with the same id and the updated balance.

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];
         //user.balance = balance;
         users[id] = User(id,balance);
    }

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

}

phyx1u5 · March 17, 2021, 9:50am

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

inzhagey · March 17, 2021, 2:03pm

I changed the memory to storage

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

kenn.eth · March 18, 2021, 4:52pm

My solution is directly accessing to the " user[id].balance " then change it to any balance you need

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;
    }

}

Ciantera_R · March 18, 2021, 7:15pm

Decoded output stores users
updated balance using
storage keyword in place
of memory keyword.

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.6;

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;
    }
}

Nigel · March 18, 2021, 8:39pm

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

I added users[id] = user; so the inputted balance would be stored in the mapping of users.

Restford · March 18, 2021, 8:42pm

Modified the updateBalance function to

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

jornack · March 19, 2021, 9:14am

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

I chose not to create a new User object, because that the object was already created in function addUser.

DJaySplash · March 19, 2021, 11:47pm

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;
    }

}

bencoin · March 20, 2021, 7:38am

My solution is to fix updateBalance() to directly access the user in the users state variable mapping.

The bug is that updateBalance() initializes and updates a temporary user with the same values as the user in the mapping, but it’s not the same struct as the user in storage, and is not persisted at the end of function execution.

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;
    }

}

lucaszanek · March 20, 2021, 10:56pm

I also not added the verification if the id exist or is provided in order to avoid an unnecesary execution of the function, in order to no extend the scope of the task.

This is my solution

  
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 {
        uint previousBalance = users[id].balance;
        users[id].balance += balance;
        assert(users[id].balance == previousBalance + balance);
    }

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

}

solich · March 21, 2021, 7:48am

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;
    }

}

STORAGE should be used here instead of memory

Samuel1 · March 21, 2021, 6:25pm

I made the code a LOT more complicated then it needed to be and got the answer wrong. I understand the concept, that memory is stored only temporarily so I will write code like this:

pragma solidity 0.7.5;
contract MemoryAndStorage{
mapping(uint => User) users; // this is key uint to value User
struct User{
uint id id;
uint balance;
}
function addUser(uint id, uint balance) public{
users[id] = Users(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;
}
}

There are other ways to solve the problem, you can simply remove the line.

ol_frank · March 22, 2021, 6:22pm

I changed, User memory user = users[id]; ----> User storage user = users[id];

bigbill · March 22, 2021, 10:02pm

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;
}

}