pragma solidity ^0.5.16;

// solhint-disable payable-fallback

/// a variant of ReadProxy.sol that's not Owned, and so has an immutable target
/// that can be used e.g. to read a oracle feed, and provide its interface, but from a
/// different address
contract ImmutableReadProxy {
    address public target;

    constructor(address _target) public {
        target = _target;
    }

    function() external {
        // The basics of a proxy read call
        // Note that msg.sender in the underlying will always be the address of this contract.
        assembly {
            calldatacopy(0, 0, calldatasize)

            // Use of staticcall - this will revert if the underlying function mutates state
            let result := staticcall(gas, sload(target_slot), 0, calldatasize, 0, 0)
            returndatacopy(0, 0, returndatasize)

            if iszero(result) {
                revert(0, returndatasize)
            }
            return(0, returndatasize)
        }
    }
}