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Patterns for Upgradeable Smart Contracts

The very essence of blockchain technology, immutability, can be a double-edged sword for smart contracts. While it guarantees security and transparency, it also makes adapting to changes and fixing bugs a challenge. Thankfully, ingenious developers have introduced upgradeability patterns to navigate this dilemma.

Why Upgrade Smart Contracts?

Imagine deploying a smart contract that governs a decentralized marketplace. As the platform evolves, you might need to:

  • Add new features: Introduce functionalities like escrow services or dispute resolution mechanisms.
  • Fix vulnerabilities: Patch critical security issues discovered after deployment.
  • Improve efficiency: Optimize the contract’s code to reduce transaction costs.

Without upgradeability patterns, addressing these needs would require deploying entirely new contracts, leading to:

  • Data migration hassles: Transferring user data and balances to the new contract can be complex and error-prone.
  • Fragmentation: Multiple contracts with the same core functionality can cause confusion and reduce network efficiency.
  • User inconvenience: Users would need to interact with a new address, potentially disrupting established workflows.

Enter the Upgradeability Patterns:

Upgradability patterns allow developers to modify the logic of a smart contract after deployment, while still maintaining the benefits of immutability. Here are two popular approaches:

  1. Proxy Pattern: This pattern introduces a proxy contract that acts as a middleman between users and the actual implementation contract. The proxy forwards function calls to the implementation contract, which contains the core logic. When an upgrade is needed, a new implementation contract is deployed, and the proxy is simply linked to the new version. This keeps the user interaction point (proxy address) constant, ensuring a seamless transition.
  2. Diamond Pattern: This advanced pattern builds upon the proxy concept, allowing for multiple facets (implementation contracts) to handle specific functionalities. Each facet can be upgraded independently, providing greater flexibility and modularity. However, the Diamond pattern is more complex to implement and requires deeper technical expertise.

Choosing the Right Pattern:

The choice between these patterns depends on various factors, including:

  • Project complexity: For simpler contracts, the Proxy pattern might suffice.
  • Upgrade frequency: If frequent upgrades are anticipated, the Diamond pattern’s modularity can be advantageous.
  • Developer expertise: Implementing the Diamond pattern requires a strong understanding of smart contract development principles.

Security Considerations:

While upgradeability patterns offer significant benefits, it’s crucial to prioritize security:

  • Centralization risks: Ensure the upgrade process is not controlled by a single entity, as this can introduce vulnerabilities.
  • Thorough testing: Rigorously test upgrades before deploying them on the mainnet to avoid introducing new bugs.
  • Transparency: Clearly communicate upgrade plans and potential risks to the community.

By understanding and adopting suitable upgradeability patterns, developers can create adaptable and future-proof smart contracts, allowing them to evolve alongside the ever-changing blockchain landscape.

Proxy pattern

Understanding the Proxy Pattern

The Proxy Pattern is a design pattern where a surrogate or placeholder is used to control access to an underlying object. In the context of smart contracts, the Proxy Pattern allows us to create a proxy contract that delegates calls to an implementation contract. This separation of concerns enables us to upgrade the implementation contract without changing the proxy contract or disrupting the contract’s state.

1. Implementation Contract (Logic Contract):

contract MyLogic {

  uint public value;

  function setValue(uint _newValue) public {
    value = _newValue;

  function getValue() public view returns(uint) {
    return value;

This contract (MyLogic) defines the core functionalities (setValue and getValue). In a real-world scenario, this would contain the actual logic of your smart contract.

2. Proxy Contract:

contract MyProxy {

  // Stores the address of the current implementation contract
  address public implementation;

  constructor(address _logic) public {
    implementation = _logic;

  // Fallback function that forwards all calls to the implementation contract
  fallback() external payable {
    address impl = implementation;
    assembly {
      let ptr := mload(0x40) // Load function pointer from memory

      // Delegate call to the implementation contract
      delegatecall(gas, impl,, msg.value, 0, 0)

      // Copy return data to memory
      let size := returndatasize
      returndatacopy(ptr, 0, size)

      // Return data to caller
      return(ptr, size)

  // Function to upgrade the logic contract (restricted access for security)
  function upgrade(address _newLogic) public {
    implementation = _newLogic;

The Proxy contract (MyProxy) acts as the entry point for users. It stores the address of the current implementation contract (implementation) in its storage.

  • The fallback function is triggered for any function call to the Proxy contract.
  • It uses assembly language to delegate the call (along with gas, data, and value) to the current implementation contract stored in implementation.
  • The return data from the implementation contract is then copied and returned to the user.


  • Users interact with the Proxy contract address.
  • The Proxy forwards all function calls to the current implementation contract.
  • When an upgrade is needed, a new implementation contract is deployed.
  • The Proxy contract’s upgrade function is used to update the implementation variable to point to the new contract address.
  • This allows the Proxy to seamlessly work with the upgraded logic without changing the user interaction point.

Important Note:

This is a simplified example for demonstration purposes. Real-world implementations would include additional features like access control for the upgrade function and proper event logging for transparency.

Remember, security is paramount. Always thoroughly test and audit your upgradeability patterns before deployment.

Diamond Pattern

Understanding the Diamond Pattern

The Diamond pattern is a design pattern for smart contracts that separates concerns into different facets or modules, each responsible for a specific aspect of the contract’s functionality. These facets are managed by a central contract, often called a Diamond or Facet Manager, which delegates calls to the appropriate facet based on the function being called.

Advantages of the Diamond Pattern

  1. Modularity: Facets can be added, removed, or upgraded without affecting the overall contract state or breaking existing functionality.
  2. Efficiency: Since each facet is responsible for a specific set of functions, contracts can be more efficient by reducing the amount of code executed for each transaction.
  3. Upgradability: The Diamond pattern allows for upgrades without requiring users to interact with a new contract address, providing a seamless experience.

Implementation Steps

  1. Diamond Contract: Create a central contract that will manage the facets. This contract should contain the logic to delegate calls to the appropriate facet based on the function signature.
  2. Facet Contracts: Implement individual facet contracts, each focusing on a specific aspect of the contract’s functionality. These contracts should contain the logic for the functions they are responsible for.
  3. Diamond Storage: Use a separate storage contract to store shared state variables. This ensures that state variables are shared among all facets.
  4. Diamond Cut: Use the Diamond Cut function to add, replace, or remove facets from the Diamond contract. This function allows for upgrades without changing the contract address.

1. Diamond (Storage) Contract:

contract Diamond {

  // Mapping to store function selectors and their corresponding facet addresses
  mapping(bytes4 => address) public functionToFacet;

  // Fallback function that forwards calls to the appropriate facet
  fallback() external payable {
    address facet = functionToFacet[msg.sig];
    require(facet != address(0), "Function not found");
    assembly {
      let ptr := mload(0x40) // Load function pointer from memory
      delegatecall(gas, facet,, msg.value, 0, 0)
      let size := returndatasize
      returndatacopy(ptr, 0, size)
      return(ptr, size)

  // Function to be called by DiamondCutFacet for upgrades
  function diamondCut(FacetCut[] calldata _facetCuts, Action _action) external {
    if (_action == Action.Add) {
    } else if (_action == Action.Remove) {
    } else if (_action == Action.Replace) {
    } else {
      revert("Invalid Action");

  // Internal functions for adding, removing, and replacing facets
  function addFacet(FacetCut[] calldata _facetCuts) internal {
    for (uint i = 0; i < _facetCuts.length; i++) {
      bytes4 selector = _facetCuts[i].functionSelectors[0];
      address facetAddress = _facetCuts[i].facet;
      functionToFacet[selector] = facetAddress;

  function removeFacet(FacetCut[] calldata _facetCuts) internal {
    for (uint i = 0; i < _facetCuts.length; i++) {
      bytes4 selector = _facetCuts[i].functionSelectors[0];
      address facetAddress = functionToFacet[selector];
      require(facetAddress != address(0), "Facet not found");
      delete functionToFacet[selector];

  function replaceFacet(FacetCut[] calldata _facetCuts) internal {
    for (uint i = 0; i < _facetCuts.length; i++) {
      bytes4 selector = _facetCuts[i].functionSelectors[0];
      address oldFacetAddress = functionToFacet[selector];
      require(oldFacetAddress != address(0), "Facet not found");
      address newFacetAddress = _facetCuts[i].facet;
      functionToFacet[selector] = newFacetAddress;

  // Enum representing the actions (add, remove, replace)
  enum Action { Add, Remove, Replace }

The Diamond contract (Diamond) acts as the core storage for the system. It maintains a mapping (functionToFacet) that links function selectors (first four bytes of a function signature) to the addresses of the corresponding facets that implement those functions.

The fallback function intercepts all user interactions. It retrieves the facet address associated with the called function’s selector and performs a delegatecall to that facet. This allows the Diamond to delegate specific functionalities to the appropriate facets.

2. Diamond Facet Cut

This contract serves as the control center for managing facet cuts. It provides functions to:

  • addFacet: Add a new facet with its associated function selectors to the Diamond contract.
  • removeFacet: Remove an existing facet and its function selectors from the Diamond contract.
  • replaceFacet: Replace an existing facet with a new one, updating the associated function selectors in the Diamond contract.
contract DiamondCutFacet {

  // Access control modifier (replace with your access control mechanism)
  modifier onlyOwner() {
    require(msg.sender == owner, "Only owner can perform this action");

  // Address of the contract owner
  address public owner;

  // Constructor (replace with your initialization logic)
  constructor(address _owner) public {
    owner = _owner;

  // Structure to define a facet cut
  struct FacetCut {
    address facet;
    bytes4[] functionSelectors;
    Action action;

  // Enum representing the actions (add, remove, replace)
  enum Action { Add, Remove, Replace }

  // Function to add a new facet with its associated function selectors
  function addFacet(FacetCut[] calldata _facetCuts) external onlyOwner {
    executeDiamondCut(_facetCuts, Action.Add);

  // Function to remove a facet and its associated function selectors
  function removeFacet(FacetCut[] calldata _facetCuts) external onlyOwner {
    executeDiamondCut(_facetCuts, Action.Remove);

  // Function to replace a facet with a new one and its associated function selectors
  function replaceFacet(FacetCut[] calldata _facetCuts) external onlyOwner {
    executeDiamondCut(_facetCuts, Action.Replace);

  // Internal function to perform the actual diamond cut operation
  function executeDiamondCut(FacetCut[] calldata _facetCuts, Action _action) internal {
    Diamond diamond = Diamond(msg.sender); // Cast the message sender to Diamond contract
    bytes memory encodedFunction = abi.encodeWithSelector(diamondsCutFunction, _facetCuts, _action);

    // Assembly call to avoid stack-too-deep errors with large facet cuts
    assembly {
      call(gas() - 700, diamond, 0, add(encodedFunction.length, 0x20), 0, 0, 0)

    require(gasleft() >= gasleft() / 100, "Insufficient gas for diamondCut"); // Gas check

  // Function selector for the diamondCut function (assumed to exist in the Diamond contract)
  bytes4 private constant diamondsCutFunction = keccak256("diamondCut(FacetCut[],Action)");

3. DiamondStorage.sol (Optional):

Although not strictly required in the Diamond pattern, a separate DiamondStorage contract can be used to centralize storage variables shared by all facets. This can improve code organization and potentially optimize storage layout.

contract DiamondStorage {

  // Your storage variables here

  uint public value;

  function setValue(uint _newValue) public {
    value = _newValue;

  function getValue() public view returns(uint) {
    return value;

4. Example Facet.sol:

This example Facet demonstrates how a facet interacts with the Diamond storage (if used) or directly with the Diamond contract’s storage (if not using a separate storage contract).

contract ExampleFacet {

  // Reference to the Diamond contract
  Diamond public diamond;

  // Constructor (replace with initialization logic)
  constructor(address _diamond) public {
    diamond = Diamond(_diamond);

  // Function utilizing the Diamond storage (if applicable)
  function getValue() public view returns(uint) {
    DiamondStorage storage ds = diamond.diamondStorage(); // Access storage if using DiamondStorage contract
    return ds.value;

  // Function utilizing the Diamond contract's storage (if not using DiamondStorage)
  function setValue(uint _newValue) public {
    diamond.diamondStorage().setValue(_newValue); // Access storage directly on Diamond contract


  • The DiamondStorage contract (optional) defines shared storage variables and functions to access and modify them.
  • The ExampleFacet contract:
    • Holds a reference to the deployed Diamond contract.
    • If using a separate DiamondStorage contract:
      • It retrieves the storage using diamondStorage() and accesses variables through it.
    • If not using a separate storage contract:
      • It directly calls the diamondStorage() function on the Diamond contract to access and modify storage variables.

Deployment and Usage:

  1. Deploy the Diamond contract.
  2. Deploy the desired Facet contracts.
  3. Use the DiamondCutFacet contract to add the deployed facets to the Diamond, specifying the function selectors they are responsible for.
  4. Interact with the Diamond contract address to utilize the functionalities provided by the added facets.


  • This is a simplified example and doesn’t cover all aspects of secure and robust Diamond implementations.
  • Thoroughly understand the Diamond pattern, implement robust access control, and conduct rigorous testing before deploying such mechanisms in production environments.


Upgradeability patterns empower developers to create evolving and future-proof smart contracts. By carefully choosing between the Proxy and Diamond patterns based on project complexity and upgrade needs, they can:

  • Fix vulnerabilities promptly, mitigating potential security risks.
  • Implement new features to enhance user experience and functionality.
  • Improve efficiency by optimizing code to reduce transaction costs.

However, it’s crucial to remember:

  • Security is paramount: Implement robust access controls, thorough testing, and transparent communication during upgrades.
  • Choose wisely: Select the pattern that best suits your project’s requirements and development expertise.

As the blockchain ecosystem continues to grow and evolve, the ability to adapt to change becomes increasingly important. Upgradeability patterns equip developers with the tools to build dynamic and responsive smart contracts, paving the way for a more resilient and future-oriented blockchain landscape.

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