Diamond.sol

Diamond.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import "@openzeppelin/contracts/proxy/Proxy.sol";

contract Diamond is Proxy{
  mapping(bytes4 => address) public implementations;

  function register( bytes4 selector, address impl ) external {
    if(impl != address(0))
      require(impl.code.length > 0);

    implementations[ selector ] = impl;
  }

  function _implementation() internal view override returns (address impl){
    impl = implementations[ msg.sig ];
    if( impl == address(0) )
      revert( "Function not registered" );
  }
}


// deploy and register these functions later

contract ImplementationA{
  function add( uint256 value1, uint256 value2 ) external pure returns( uint256 sum ){
    sum = value1 + value2;
  }

  function sub( uint256, uint256 ) external pure returns( uint256 diff ){
    revert( "not implemented" );
  }
}


// deploy and register these functions later

contract ImplementationB {
  function mul( uint256 value1, uint256 value2 ) external pure returns( uint256 product ){
    product = value1 * value2;
  }
}