Transient Storage

Let’s say that we are implementing that we want to reuse some data between two or more hooks in one same transaction.

For example, we want to reuse the same data between the beforeSwap and afterSwap.

We could use a global variable but this has two main issues:

• It is not gas efficient (saving to persistent storage is the most expensive operation in the blockchain)
• It is not secure (it might be vulnerable to reentrancy attacks)

What is transient storage?

Transient storage is a feature that allows us to store data in memory that is only valid for the current transaction.

It doesn’t persist across transactions, it is not visible to other contracts and it is much cheaper to use than persistent storage.

EIP-1153  was the proposal to implement it in the EVM. It was included in the Cancun  hard fork.

Solidity 0.8.24 was the first version to support transient storage with inline assembly and tload and tstore instructions. And since 0.8.28  it is supported as storage state variables of value types.

contract TransientStorageReentrancyGuard {
    mapping(address => bool) sentGifts;
    bool transient locked;
 
    modifier nonReentrant {
        require(!locked, "Reentrancy attempt");
        locked = true;
        _;
        locked = false;
    }

How can we leverage it?

We can use transient storage to store the data between different hooks.

WIP…