Diamond pattern (EIP-2535) in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the DiamondCutFacet contract.

Blockchain / Solidity

contract DiamondCutFacet is IDiamondCut {
    function diamondCut(
        IDiamondCut.FacetCut[] memory _diamondCut,
        address _init,
        bytes memory _calldata
    ) external override [1] {
        // Implementation
    }
}

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

Apure

Bpublic

Cexternal

Dinternal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'public' instead of 'external' causes mismatch with interface.

Using 'internal' or 'private' makes the function inaccessible externally.

The diamondCut function must be declared as external to match the interface and allow external calls.

2fill in blank

medium

Complete the code to add a facet address to the diamond storage.

Blockchain / Solidity

library LibDiamond {
    struct FacetAddressAndSelectorPosition {
        address facetAddress;
        uint16 selectorPosition;
    }

    struct DiamondStorage {
        mapping(bytes4 => FacetAddressAndSelectorPosition) selectorToFacetAndPosition;
        address[] facetAddresses;
    }

    function diamondStorage() internal pure returns (DiamondStorage storage ds) {
        bytes32 position = keccak256("diamond.standard.diamond.storage");
        assembly {
            ds.slot := position
        }
    }

    function addFacetAddress(address _facetAddress) internal {
        DiamondStorage storage ds = diamondStorage();
        ds.facetAddresses.[1](_facetAddress);
    }
}

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

Apush

Bappend

Cadd

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which is not a Solidity array method.

Using 'add' or 'insert' which do not exist for arrays.

To add an element to a dynamic array in Solidity, use the push method.

3fill in blank

hard

Fix the error in the diamondCut function signature to match the interface.

Blockchain / Solidity

function diamondCut(
    IDiamondCut.FacetCut[] memory _diamondCut,
    address _init,
    bytes memory _calldata
) external override [1] {
    // Implementation
}

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

Apure

Bpayable

Cview

Dnonpayable

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting 'payable' causes the function to reject Ether transfers.

Using 'pure' or 'view' is incorrect because the function modifies state.

The diamondCut function must be declared payable to accept Ether during the call, as per the EIP-2535 specification.

4fill in blank

hard

Fill both blanks to complete the diamondCut function call and event emission.

Blockchain / Solidity

function diamondCut(
    IDiamondCut.FacetCut[] memory _diamondCut,
    address _init,
    bytes memory _calldata
) external override payable {
    LibDiamond.diamondCut(_diamondCut, _init, _calldata);
    emit [1](_diamondCut, _init, _calldata);
}

// Event declaration
event [2](IDiamondCut.FacetCut[] _diamondCut, address _init, bytes _calldata);

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ADiamondCut

BCutDiamond

CDiamondUpdate

DCutEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect event names causes compilation or runtime errors.

Mismatch between event declaration and emission.

The event emitted after diamondCut is named DiamondCut as per the EIP-2535 standard.

5fill in blank

hard

Fill all three blanks to complete the diamondCut function call with correct parameters and event emission.

Blockchain / Solidity

function diamondCut(
    IDiamondCut.FacetCut[] memory [1],
    address [2],
    bytes memory [3]
) external override payable {
    LibDiamond.diamondCut([1], [2], [3]);
    emit DiamondCut([1], [2], [3]);
}

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

A_diamondCut

B_init

C_calldata

D_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent parameter names causes errors.

Using '_data' instead of '_calldata' is incorrect.

The parameters and event arguments must use the exact variable names _diamondCut, _init, and _calldata as declared.

Practice

1.

What is the main purpose of the Diamond pattern (EIP-2535) in blockchain smart contracts?

easy

A. To split a large contract into smaller, manageable facets

B. To increase the gas cost of contract deployment

C. To prevent any contract upgrades

D. To combine multiple unrelated contracts into one

Solution

1. Step 1: Understand the Diamond pattern concept

   The Diamond pattern divides a big contract into smaller parts called facets to organize code better.

2. Step 2: Identify the main benefit

   This splitting allows easier upgrades and management of smart contracts.

3. Final Answer:

   To split a large contract into smaller, manageable facets -> Option A

4. Quick Check:

   Diamond pattern = splitting contract into facets [OK]

Hint: Remember: Diamond pattern breaks big contracts into smaller parts [OK]

Common Mistakes:

• Thinking it prevents upgrades
• Assuming it increases deployment cost
• Confusing it with contract merging

2.

Which of the following is the correct Solidity syntax to declare a facet interface in the Diamond pattern?

interface IFacet {
    function myFunction() external;
}

easy

A. contract IFacet { function myFunction() public {} }

B. interface IFacet { function myFunction() external; }

C. library IFacet { function myFunction() internal; }

D. struct IFacet { function myFunction() external; }

Solution

1. Step 1: Identify correct Solidity declaration for interface

   Interfaces use the keyword interface and declare functions without bodies.

2. Step 2: Match function visibility and syntax

   Function in interface must be external and end with a semicolon, no body.

3. Final Answer:

   interface IFacet { function myFunction() external; } -> Option B

4. Quick Check:

   Interface syntax = interface IFacet { function myFunction() external; } [OK]

Hint: Interfaces have no function bodies and use 'external' functions [OK]

Common Mistakes:

• Using contract instead of interface
• Adding function bodies in interface
• Using wrong visibility like public or internal

3.

Given the following Solidity snippet using the Diamond pattern, what will be the output when calling diamond.facetFunction()?

contract FacetA {
    function facetFunction() external pure returns (string memory) {
        return "Facet A called";
    }
}

contract Diamond {
    FacetA facetA;
    constructor() {
        facetA = new FacetA();
    }
    function facetFunction() external view returns (string memory) {
        return facetA.facetFunction();
    }
}

medium

A. "Facet A called"

B. Compilation error due to missing function

C. "Diamond called"

D. Runtime error: function not found

Solution

1. Step 1: Understand contract interaction

   The Diamond contract creates an instance of FacetA and calls its facetFunction.

2. Step 2: Trace the function call and return value

   Calling diamond.facetFunction() returns the string from FacetA: "Facet A called".

3. Final Answer:

   "Facet A called" -> Option A

4. Quick Check:

   Diamond calls FacetA function = "Facet A called" [OK]

Hint: Diamond delegates calls to facets returning their outputs [OK]

Common Mistakes:

• Assuming Diamond returns its own string
• Expecting compilation error due to delegation
• Confusing runtime errors with correct delegation

4.

Identify the error in this simplified Diamond pattern Solidity code snippet:

contract Diamond {
    mapping(bytes4 => address) public facets;

    function addFacet(bytes4 selector, address facetAddress) public {
        facets[selector] = facetAddress;
    }

    fallback() external {
        address facet = facets[msg.sig];
        (bool success, ) = facet.delegatecall(msg.data);
        require(success, "Delegatecall failed");
    }
}

medium

A. Using delegatecall instead of call

B. Fallback function must be external payable

C. Mapping key type should be bytes32, not bytes4

D. Missing return statement in fallback function

Solution

1. Step 1: Analyze fallback function behavior

   The fallback uses delegatecall but does not return data to the caller.

2. Step 2: Identify missing return data forwarding

   Delegatecall returns data that must be returned by fallback to preserve call behavior.

3. Final Answer:

   Missing return statement in fallback function -> Option D

4. Quick Check:

   Fallback must return delegatecall data [OK]

Hint: Fallback must return delegatecall results to caller [OK]

Common Mistakes:

• Ignoring return data in fallback
• Confusing delegatecall with call
• Assuming payable is mandatory for fallback

5.

You want to upgrade a Diamond contract by adding a new facet with a function selector that already exists in another facet. What will happen if you do not remove the old selector before adding the new one?

hard

A. The Diamond will route calls to the new facet for that selector

B. The Diamond will have two facets for the same selector causing ambiguity

C. The old facet's function will still be called, ignoring the new one

D. The contract will fail to compile due to duplicate selectors

Solution

1. Step 1: Understand selector uniqueness in Diamond pattern

   Each function selector maps to exactly one facet address in the Diamond.

2. Step 2: Analyze what happens when adding duplicate selectors

   If you add a selector without removing the old one, the mapping still points to the old facet, so calls route there.

3. Final Answer:

   The old facet's function will still be called, ignoring the new one -> Option C

4. Quick Check:

   Duplicate selector without removal = old facet called [OK]

Hint: Remove old selector before adding new to update facet [OK]

Common Mistakes:

• Assuming Diamond supports multiple facets per selector
• Expecting compile-time errors for duplicates
• Thinking new facet automatically overrides old without removal