《纸上谈兵·solidity》第 18 课：合约设计模式实战（三）—— 代理 + 插件化架构（Diamond Standard / EIP-2535）

library LibAppStorage {
    bytes32 constant DIAMOND_STORAGE_POSITION = keccak256("diamond.standard.app.storage");

    struct AppStorage {
        uint256 value;
        mapping(address => uint256) balances;
    }

    function diamondStorage() internal pure returns (AppStorage storage ds) {
        bytes32 position = DIAMOND_STORAGE_POSITION;
        assembly {
            ds.slot := position
        }
    }
}

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

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

    modifier onlyOwner() {
        require(msg.sender == owner, "Not owner");
        _;
    }

    constructor() {
        owner = msg.sender;
    }

    function addFacet(bytes4 selector, address facet) external onlyOwner {
        facets[selector] = facet;
    }

    fallback() external payable {
        address facet = facets[msg.sig];
        require(facet != address(0), "Function not found");

        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 {}
}

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

contract FacetA {
    uint256 public value;

    function setValue(uint256 _v) external {
        value = _v;
    }
}

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

contract FacetB {
    uint256 public number;

    function add(uint256 a, uint256 b) external returns (uint256) {
        number = a + b;
        return number;
    }
}

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

import "forge-std/Test.sol";
import "../src/Diamond.sol";
import "../src/FacetA.sol";
import "../src/FacetB.sol";

contract DiamondTest is Test {
    Diamond diamond;
    FacetA facetA;
    FacetB facetB;

    function setUp() public {
        diamond = new Diamond();
        facetA = new FacetA();
        facetB = new FacetB();

        diamond.addFacet(FacetA.setValue.selector, address(facetA));
        diamond.addFacet(FacetB.add.selector, address(facetB));
    }

    function testFacetACall() public {
        (bool ok, ) = address(diamond).call(
            abi.encodeWithSelector(FacetA.setValue.selector, 42)
        );
        assertTrue(ok, "FacetA call failed");
    }

    function testFacetBCall() public {
        (bool ok, bytes memory data) = address(diamond).call(
            abi.encodeWithSelector(FacetB.add.selector, 1, 2)
        );
        assertTrue(ok, "FacetB call failed");
        uint256 result = abi.decode(data, (uint256));
        assertEq(result, 3);
    }
}

➜  tutorial git:(main) ✗ forge test --match-path test/Diamond.t.sol -vvv      

[⠊] Compiling...
[⠒] Compiling 4 files with Solc 0.8.30
[⠑] Solc 0.8.30 finished in 522.72ms
Compiler run successful!

Ran 2 tests for test/Diamond.t.sol:DiamondTest
[PASS] testFacetACall() (gas: 33464)
[PASS] testFacetBCall() (gas: 34743)
Suite result: ok. 2 passed; 0 failed; 0 skipped; finished in 4.38ms (1.35ms CPU time)

Ran 1 test suite in 162.88ms (4.38ms CPU time): 2 tests passed, 0 failed, 0 skipped (2 total tests)