Pure Function to get Proxy Storage in Upgradeable contracts

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1

I have a general question regarding the OZ Proxies.

Why are you using a pure function to get the contract storage location and not a view function?

For example in https://github.com/OpenZeppelin/openzeppelin-contracts-upgradeable/blob/v5.0.2/contracts/access/OwnableUpgradeable.sol#L30

      function _getOwnableStorage() private pure returns (OwnableStorage storage $) {
        assembly {
            $.slot := OwnableStorageLocation
        }
    }

I always thought a pure function shouldn't access state variables, or does simply accessing a constant (OwnableStorageLocation) and returning storage not count as a state variable access. What's happening under the hood here after compilation? And why isn't the compiler complaining about the access in a pure function?

2

This function does not access any state variable. It only computes the storage pointer by reading a constant.

You can see, for example, that after getting this storage pointer, reading the actual storage variable from the struct is view: https://github.com/OpenZeppelin/openzeppelin-contracts-upgradeable/blob/v5.0.2/contracts/access/OwnableUpgradeable.sol#L73-L76