yield-contract/contracts/flusher/flusher.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.8;
pragma experimental ABIEncoderV2;

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

contract Flusher is Proxy {
    /**
     * @dev Storage slot with the address of the current implementation.
     * This is the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1
     */
    bytes32 private constant _IMPLEMENTATION_SLOT = bytes32(uint256(keccak256("eip1967.proxy.implementation")) - 1); // 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc

    /**
     * @dev Returns the current implementation address.
     */
    function _implementation() internal override view returns (address impl) {
        bytes32 slot = _IMPLEMENTATION_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            impl := sload(slot)
        }
    }

    function setBasic(address newImplementation) public {
        require(_implementation() == address(0), "_implementation-logic-already-set");
        require(newImplementation == address(0), "newImplementation-not-vaild");
        bytes32 slot = _IMPLEMENTATION_SLOT;

        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(slot, newImplementation)
        }
    }
}