SlotDerivation

_Library for computing storage (and transient storage) locations from namespaces and deriving slots corresponding to standard patterns. The derivation method for array and mapping matches the storage layout used by the solidity language / compiler.

See https://docs.soliditylang.org/en/v0.8.20/internals/layout_in_storage.html#mappings-and-dynamic-arrays[Solidity docs for mappings and dynamic arrays.].

Example usage:

contract Example {
    // Add the library methods
    using StorageSlot for bytes32;
    using SlotDerivation for bytes32;

    // Declare a namespace
    string private constant _NAMESPACE = "<namespace>" // eg. OpenZeppelin.Slot

    function setValueInNamespace(uint256 key, address newValue) internal {
        _NAMESPACE.erc7201Slot().deriveMapping(key).getAddressSlot().value = newValue;
    }

    function getValueInNamespace(uint256 key) internal view returns (address) {
        return _NAMESPACE.erc7201Slot().deriveMapping(key).getAddressSlot().value;
    }
}

TIP: Consider using this library along with {StorageSlot}.

NOTE: This library provides a way to manipulate storage locations in a non-standard way. Tooling for checking upgrade safety will ignore the slots accessed through this library.

Available since v5.1._

erc7201Slot

function erc7201Slot(string namespace) internal pure returns (bytes32 slot)

Derive an ERC-7201 slot from a string (namespace).

offset

function offset(bytes32 slot, uint256 pos) internal pure returns (bytes32 result)

Add an offset to a slot to get the n-th element of a structure or an array.

deriveArray

function deriveArray(bytes32 slot) internal pure returns (bytes32 result)

Derive the location of the first element in an array from the slot where the length is stored.