std-storage

https://book.getfoundry.sh/reference/forge-std/std-storage.html

stdstore

Query functions:

• target: Set the address of the contract (required)

• sig: Set the signature of the function to call (required)

• with_key: Set the mapping key, if the variable is of type mapping

• depth: Set the index of the struct member, if the variable is of type struct

Terminator functions:

• checked_write: Set the data to be written to the storage slot(s)

• find: Return the slot number

Example 1

playerToCharacter tracks each player's character's stats.

// MetaRPG.sol

struct Character {
    Class class;
    uint256 level;
    uint256 xp;
}

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(metaRpg.playerToCharacter.selector)
    .with_key(address(this))
    .depth(1)
    .checked_write(120);

Example 2

function setUp() public virtual {
        dai = new Dai(4);
        vm.label(address(dai), "dai contract");

        weth = new WETH9();
        vm.label(address(weth), "weth contract");

        //mint 100 DAI for Vault
        vault = new Vault(address(dai), address(weth), address(priceFeed),8,10);
        vm.label(address(vault), "vault contract");
        
        // dai.mint(address(vault), 10000*10**18);
        //......accessing stdstore instance........\\
        stdstore    
        .target(address(dai))
        .sig(dai.balanceOf.selector)    //select balanceOf mapping
        .with_key(address(vault))       //set mapping key balanceOf(address(vault))
        .checked_write(10000*10**18);   //data to be written to the storage slot -> balanceOf(address(vault)) = 10000*10**18

.selector

• https://ethereum.stackexchange.com/questions/72687/explanation-of-appending-selector-in-solidity-smart-contracts
• A function selector is the first four bytes of the calldata that specifies which function to call during a function call

.selector returns the ABI function selector.

The first four bytes of the call data for a function call specifies the function to be called. It is the first (left, high-order in big-endian) four bytes of the Keccak-256 (SHA-3) hash of the signature of the function. The signature is defined as the canonical expression of the basic prototype without data location specifier, i.e. the function name with the parenthesised list of parameter types. Parameter types are split by a single comma - no spaces are used.

• https://ethereum.stackexchange.com/questions/72687/explanation-of-appending-selector-in-solidity-smart-contracts
• https://ethereum.stackexchange.com/questions/72363/what-is-a-function-selector