Simple delegate-proxy implementation

Proxy.sol

pragma solidity ^0.4.24;

contract Proxy {

	// Default delegatecall target
	address destination;

	/**
	 * @dev Constructor. Sets the default destination
	 * @param _dest The address to which this contract will forward execution
	 */
	constructor (address _dest) public {
		destination = _dest;
	}

	/**
	 * @dev Fallback function. Delegates all execution to the default address
	 */
	function () external payable {
		address target = destination;
		assembly {
			calldatacopy(0, 0, calldatasize) // Copy msg.data to memory

			// Delegatecall the target, sending msg.data
			let ret := delegatecall(gas, target, 0, calldatasize, 0, 0)

			returndatacopy(0, 0, returndatasize) // Copy returned data to memory

			// If the delegatecall failed (ret == 0), revert data.
			// Otherwise, return data
			switch ret
			case 0 { revert(0, returndatasize) }
			default { return(0, returndatasize) }
		}
	}
}