diamond-pattern

EIP-2535 Diamond Pattern

Overview

The Diamond pattern splits a contract into multiple "facets" (logic modules) that share a single storage and address. Bypasses the 24KB contract size limit and enables surgical upgrades of individual functions.

Architecture

User → Diamond Proxy
         ├── FacetA (functions a1, a2)
         ├── FacetB (functions b1, b2, b3)
         ├── DiamondCutFacet (add/replace/remove functions)
         └── DiamondLoupeFacet (introspection)

All facets share the Diamond's storage context via delegatecall.

Diamond Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {LibDiamond} from "./libraries/LibDiamond.sol";

contract Diamond {
    constructor(address contractOwner, address diamondCutFacet) payable {
        LibDiamond.setContractOwner(contractOwner);
        LibDiamond.FacetCut[] memory cut = new LibDiamond.FacetCut[](1);
        bytes4[] memory selectors = new bytes4[](1);
        selectors[0] = IDiamondCut.diamondCut.selector;
        cut[0] = LibDiamond.FacetCut({
            facetAddress: diamondCutFacet,
            action: LibDiamond.FacetCutAction.Add,
            functionSelectors: selectors
        });
        LibDiamond.diamondCut(cut, address(0), "");
    }

    fallback() external payable {
        LibDiamond.DiamondStorage storage ds = LibDiamond.diamondStorage();
        address facet = ds.selectorToFacetAndPosition[msg.sig].facetAddress;
        require(facet != address(0), "Diamond: Function does not exist");
        assembly {
            calldatacopy(0, 0, calldatasize())
            let result := delegatecall(gas(), facet, 0, calldatasize(), 0, 0)
            returndatacopy(0, 0, returndatasize())
            switch result
            case 0 { revert(0, returndatasize()) }
            default { return(0, returndatasize()) }
        }
    }

    receive() external payable {}
}

DiamondCut Interface

interface IDiamondCut {
    enum FacetCutAction { Add, Replace, Remove }

    struct FacetCut {
        address facetAddress;
        FacetCutAction action;
        bytes4[] functionSelectors;
    }

    event DiamondCut(FacetCut[] diamondCut, address init, bytes calldata);

    function diamondCut(
        FacetCut[] calldata diamondCut_,
        address init_,
        bytes calldata calldata_
    ) external;
}