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pragma solidity 0.5.11;
* @title DharmaUpgradeBeacon
* @author 0age
* @notice This contract holds the address of the current implementation for
* Dharma smart wallets and lets a controller update that address in storage.
contract DharmaUpgradeBeacon {
// The implementation address is held in storage slot zero.
address private _implementation;
// The controller that can update the implementation is set as a constant.
address private constant _CONTROLLER = address(
* @notice In the fallback function, allow only the controller to update the
* implementation address - for all other callers, return the current address.
* Note that this requires inline assembly, as Solidity fallback functions do
* not natively take arguments or return values.
function () external {
// Return implementation address for all callers other than the controller.
if (msg.sender != _CONTROLLER) {
// Load implementation from storage slot zero into memory and return it.
assembly {
mstore(0, sload(0))
return(0, 32)
} else {
// Set implementation - put first word in calldata in storage slot zero.
assembly { sstore(0, calldataload(0)) }
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