Std Storage

Std Storage is a library that makes manipulating storage easy.

To use Std Storage, import the following in your test contract:

import {stdStorage, StdStorage} from "forge-std/Test.sol";

Add the following line in your test contract:

using stdStorage for StdStorage;

Then, access Std Storage via the stdstore instance.

Functions

Query functions:

  • target: Set the address of the target contract
  • sig: Set the 4-byte selector of the function to static call
  • with_key: Pass an argument to the function (can be used multiple times)
  • depth: Set the position of the value in the tuple (e.g. inside a struct)

Terminator functions:

  • find: Return the slot number
  • checked_write: Set the data to be written to the storage slot(s)
  • read_<type>: Read the value from the storage slot as <type>

Example

playerToCharacter tracks info about players’ characters.

// MetaRPG.sol

struct Character {
    string name;
    uint256 level;
}

mapping (address => Character) public playerToCharacter;

Let’s say we want to set the level of our character to 120.

// MetaRPG.t.sol

stdstore
    .target(address(metaRpg))
    .sig("playerToCharacter(address)")
    .with_key(address(this))
    .depth(1)
    .checked_write(120);

Limitations

  • Accessing packed slots is not supported

Known issues

  • Slot(s) may not be found if the tuple contains types shorter than 32 bytes