is there a posible storage clash in smallProxy.sol that uses "delegateCall" between _IMPLEMENTATION_SLOT and value variables?

[albatros-github]

why in the smallProxy.sol that uses "delegateCall" from import "@openzeppelin/contracts/proxy/Proxy.sol"; the vasriable "bytes32 private constant _IMPLEMENTATION_SLOT" doesn't clash with the implementation contract variable "uint256 public value;"

[krakxn]

Code snippet for each please.

[albatros-github]

The smallproxy uses the _delegate function from inherited proxy, that is just a delegatecall(...)

"_IMPLEMENTATION_SLOT" is a bytes32, the base position is stored in the first storage slot (0), so the "value" variable in the storage of contract implementation that is inside smallProxy.sol and that is called by delegatecall should corrupt the storage position 0 in the smallProxy

SmallProxy.sol:

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

contract SmallProxy is Proxy {
// This is the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1
bytes32 private constant _IMPLEMENTATION_SLOT =
0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;

...
contract ImplementationA {
uint256 public value;

...

contract ImplementationB {
uint256 public value;
`

• proxy.sol:

function _delegate(address implementation) internal virtual { assembly { calldatacopy(0, 0, calldatasize()) ... let result := delegatecall(gas(), implementation, 0, calldatasize(), 0, 0)

[albatros-github]

@krakxn there is no "storage" collision because for the constant and immutable state variables "The compiler does not reserve a storage slot for these variables, and every occurrence is replaced by the respective value." so those values are saved in the contract's deployed code itself.

Patrick talk about this in the minute 12:10:15 of the 32 hours video and this detail is in the solidity docs in "contracts" section. Just a note: a non constant bytes state variable would have a storage slot in the EVM layout and then it could be participant in a storage collision.

[krakxn]

Yes! It also helps to save gas costs as it is hard-coded in the compiled contract, unlike storage variables which have the inherent property of being modified.