Proxy pattern (upgradeable contracts) in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the proxy contract's storage variable for the implementation address.

Blockchain / Solidity

address public [1];

Drag options to blanks, or click blank then click option'

Aowner

Bimplementation

Cproxy

Dadmin

Attempts:

3 left

💡 Hint

Common Mistakes

Using owner or admin instead of implementation.

Forgetting to declare the variable as public.

The proxy contract stores the address of the implementation contract in a variable named implementation.

2fill in blank

medium

Complete the fallback function to delegate calls to the implementation contract.

Blockchain / Solidity

fallback() external payable {
    (bool success, ) = [1].delegatecall(msg.data);
    require(success, "Delegatecall failed");
}

Drag options to blanks, or click blank then click option'

Aimplementation

Bowner

Cmsg.sender

Daddress(this)

Attempts:

3 left

💡 Hint

Common Mistakes

Using owner or msg.sender instead of implementation.

Using call instead of delegatecall.

The fallback function uses delegatecall to forward calls to the implementation contract.

3fill in blank

hard

Fix the error in the upgrade function to correctly update the implementation address.

Blockchain / Solidity

function upgradeTo(address newImplementation) external {
    require(newImplementation != address(0), "Invalid address");
    [1] = newImplementation;
}

Drag options to blanks, or click blank then click option'

Aowner

Badmin

Cproxy

Dimplementation

Attempts:

3 left

💡 Hint

Common Mistakes

Updating owner or admin instead of implementation.

Not checking for zero address before upgrade.

The upgrade function must update the implementation address to the new contract address.

4fill in blank

hard

Fill both blanks to create a mapping for admin addresses and a modifier to restrict access.

Blockchain / Solidity

mapping(address => bool) public [1];

modifier only[2]() {
    require(admins[msg.sender], "Not admin");
    _;
}

Drag options to blanks, or click blank then click option'

Aadmins

Bowners

CAdmins

DOwners

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent names between mapping and modifier.

Not capitalizing the modifier name correctly.

The mapping is named admins and the modifier is onlyAdmins to restrict function calls to admins.

5fill in blank

hard

Fill all three blanks to write a dictionary comprehension that maps function selectors to implementation addresses if the selector is valid.

Blockchain / Solidity

mapping(bytes4 => address) public [1] = {
    [2]: [3] for selector in selectors if isValid(selector)
};

Drag options to blanks, or click blank then click option'

AselectorToImpl

Bselector

Cimplementation

Dselectors

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable names for keys or values.

Confusing the iterable selectors with the key variable selector.

This comprehension creates a mapping named selectorToImpl from each valid selector to the implementation address.