Diamond pattern (EIP-2535) in Blockchain / Solidity - Mini Project: Build & Apply

Diamond Pattern (EIP-2535) Basic Setup

📖 Scenario: You are building a modular smart contract system using the Diamond pattern (EIP-2535). This pattern allows you to split your contract logic into multiple smaller contracts called facets, which can be added, replaced, or removed dynamically.This project guides you through creating a simple diamond contract with one facet and then adding a function selector to it.

🎯 Goal: Build a basic diamond contract setup with one facet and add a function selector to the diamond's selector set.

📋 What You'll Learn

Create a diamond storage struct to hold facet addresses and selectors

Define a facet contract with one function

Add a function selector to the diamond storage

Print the selector to verify it was added

💡 Why This Matters

🌍 Real World

The Diamond pattern is used in blockchain to build upgradeable and modular smart contracts that can grow and change without losing state.

💼 Career

Understanding EIP-2535 is valuable for blockchain developers working on complex decentralized applications requiring modularity and upgradeability.

1

Create Diamond Storage Struct

Create a struct called DiamondStorage with a mapping(bytes4 => address) facets to store function selectors and their facet addresses. Then create a function diamondStorage() that returns a storage pointer to DiamondStorage at a fixed slot.

Blockchain / Solidity

// Your code here

Hint

Use mapping(bytes4 => address) inside the struct to map selectors to facet addresses. Use keccak256 to get a unique storage slot and inline assembly to assign it.

2

Create a Facet Contract with One Function

Create a contract called SimpleFacet with a public function hello() that returns the string "Hello, Diamond!".

Blockchain / Solidity

pragma solidity ^0.8.19;

struct DiamondStorage {
    mapping(bytes4 => address) facets;
}

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

// Create SimpleFacet contract with hello() function
// Your code here

Hint

Define a contract with a simple public function that returns a fixed string.

3

Add Function Selector to Diamond Storage

Inside a new contract called Diamond, create a function addFacet() that stores the address of SimpleFacet for the selector of hello() in the diamond storage mapping facets. Use diamondStorage() to access storage. Use SimpleFacet.hello.selector to get the selector.

Blockchain / Solidity

pragma solidity ^0.8.19;

struct DiamondStorage {
    mapping(bytes4 => address) facets;
}

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

contract SimpleFacet {
    function hello() public pure returns (string memory) {
        return "Hello, Diamond!";
    }
}

// Create Diamond contract with addFacet() function
// Your code here

Hint

Use the diamond storage function to get storage, then assign the facet address to the selector key.

4

Print the Stored Selector Address

In the Diamond contract, add a public view function getFacetAddress() that takes a bytes4 selector and returns the facet address from diamond storage. Then write a script to deploy SimpleFacet and Diamond, call addFacet() with the SimpleFacet address, and print the address returned by getFacetAddress(SimpleFacet.hello.selector).

Blockchain / Solidity

pragma solidity ^0.8.19;

struct DiamondStorage {
    mapping(bytes4 => address) facets;
}

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

contract SimpleFacet {
    function hello() public pure returns (string memory) {
        return "Hello, Diamond!";
    }
}

contract Diamond {
    function addFacet(address facetAddress) public {
        DiamondStorage storage ds = diamondStorage();
        ds.facets[SimpleFacet.hello.selector] = facetAddress;
    }

    // Add getFacetAddress function here
    // Your code here
}

// Add deployment and print script here
// Your code here

Hint

Write a getter function to read from diamond storage. Then simulate deployment and calls to add and retrieve the facet address.

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