Balance

ETH is stored in the World contract and owned by namespaces. Any ETH sent with a call to a System is kept on the World, and credited to the namescape to which the System belongs. This has two important effects:

The ETH balance is shared between the different System contracts in the same namespace of the same World.
The same System can be used in multiple World contracts and the ETH balances remain separate.

To know how much ETH a call has included a System can check _msgValue() (opens in a new tab).

To know how much ETH a specific namespace has you can look in world:Balances (the Balances table of the world namespace).

import { Balances } from "@latticexyz/world/src/codegen/tables/Balances.sol";
 
uint256 balance = Balances.get(<namespace>);

See this in action

Have a MUD application running. The easiest way to do this is to run the template locally.
Here we are not concerned with the client, so change to the contracts page. Because we are not concerned with the client, all the file names will be relative to .../packages/contracts.
```
cd packages/contracts
```

Create a .env file with:

PRIVATE_KEY - the private key of an account that has ETH on the blockchain.
WORLD_ADDRESS - the address of the World to which you add the namespace.

If you are using the template with a fresh pnpm dev, then you can use this .env:

.env

# Anvil default private key for the second account
# (NOT the account that deployed the World)
PRIVATE_KEY=0x59c6995e998f97a5a0044966f0945389dc9e86dae88c7a8412f4603b6b78690d
 
# Address for the world we are extending
WORLD_ADDRESS=0x6e9474e9c83676b9a71133ff96db43e7aa0a4342

Create this file as scripts/GetBalance.s.sol.

GetBalance.s.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.21;
 
import { Script } from "forge-std/Script.sol";
import { console } from "forge-std/console.sol";
import { Balances } from "@latticexyz/world/src/codegen/tables/Balances.sol";
import { StoreSwitch } from "@latticexyz/store/src/StoreSwitch.sol";
import { ResourceId } from "@latticexyz/store/src/ResourceId.sol";
import { WorldResourceIdLib } from "@latticexyz/world/src/WorldResourceId.sol";
 
contract GetBalance is Script {
  function run() external {
    address worldAddress = vm.envAddress("WORLD_ADDRESS");
    StoreSwitch.setStoreAddress(worldAddress);
    console.log("World at:", worldAddress);
    ResourceId namespaceResource = WorldResourceIdLib.encodeNamespace(bytes14(""));
    console.log("Namespace ID: %x", uint256(ResourceId.unwrap(namespaceResource)));
    uint256 balance = Balances.get(namespaceResource);
    console.log("Balance: %d wei", balance);
  }
}

Explanation

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.21;

Standard Solidity boilerplate

import { Script } from "forge-std/Script.sol";
import { console } from "forge-std/console.sol";

Standard forge script (opens in a new tab) boilerplate.

import { Balances } from "@latticexyz/world/src/codegen/tables/Balances.sol";

The Balances table contains namespace balances. Note that while this table's Solidity code is available as part of the library, it is a standard MUD table and as such gets created from a mud.config.ts file (opens in a new tab).

import { StoreSwitch } from "@latticexyz/store/src/StoreSwitch.sol";

We need this file (opens in a new tab) to specify the World's address.

import { ResourceId } from "@latticexyz/store/src/ResourceId.sol";
import { WorldResourceIdLib } from "@latticexyz/world/src/WorldResourceId.sol";

We need the namespace's ResourceId.

contract GetBalance is Script {
    function run() external {
        address worldAddress = vm.envAddress("WORLD_ADDRESS");

Get WORLD_ADDRESS from .env.

       StoreSwitch.setStoreAddress(worldAddress);
       console.log("World at:", worldAddress);

Set the address of the World (opens in a new tab) so future data calls to go to the correct location.

       ResourceId namespaceResource = WorldResourceIdLib.encodeNamespace(bytes14(""));
       console.log("Namespace ID: %x", uint256(ResourceId.unwrap(namespaceResource)));

Create the ResourceId for the root namespace.

       uint256 balance = Balances.get(namespaceResource);
       console.log("Balance: %d wei", balance);
   }
}

Finally, get the balance from the world:Balances table.

Source the .env file (we are going to use the variables there to transfer ETH to the root namespace's account).
```
source .env
```

Run the script.

forge script script/GetBalance.s.sol --rpc-url http://localhost:8545

The balance should be zero for now.

To allow increment to accept wei, edit src/systems/IncrementSystem.sol to make it payable:

IncrementSystem.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.21;
 
import { System } from "@latticexyz/world/src/System.sol";
import { Counter } from "../codegen/index.sol";
 
contract IncrementSystem is System {
  function increment() public payable returns (uint32) {
    uint32 counter = Counter.get();
    uint32 newValue = counter + 1;
    Counter.set(newValue);
    return newValue;
  }
}

pnpm dev deploys the new code, but it deploys it to a new World. Restart pnpm dev to have a World in the same address as before.

Call increment with ETH.

cast send --private-key $PRIVATE_KEY 0x6E9474e9c83676B9A71133FF96Db43E7AA0a4342 --value 1ether "increment()"

Run the script again to see that the balance is higher.

forge script script/GetBalance.s.sol --rpc-url http://localhost:8545

To transfer ETH out of the World you need to have the access permission level to the namespace itself. Note that System contracts within the namespace do have that permission.

You use either transferBalanceToNamespace (opens in a new tab), if you want to transfer between namespaces in the same World, or transferBalanceToAddress (opens in a new tab), to transfer to a different address.

See this in action

These steps assume you already transferred 1 ether to the root namespace.

Run this command to transfer 10 wei to the zero address.

cast send --private-key $PRIVATE_KEY 0x6E9474e9c83676B9A71133FF96Db43E7AA0a4342 "transferBalanceToAddress(bytes32,address,uint256)" 0x6e73000000000000000000000000000000000000000000000000000000000000 `cast address-zero` 10

See that the namespace's balance is lower by 10 wei.

forge script script/GetBalance.s.sol --rpc-url http://localhost:8545

See that 10 wei have been deducted from the balance of the World.
```
cast balance $WORLD_ADDRESS
```

If you need to transfer ETH in a System that has access to a namespace (for example, because it is in that namespace), you can use a function similar to this:

function _transfer(address to, uint amount) private {
  IWorld(_world()).transferBalanceToAddress(WorldResourceIdLib.encodeNamespace("<namespace goes here>"), to, amount);
}

Function Selectors Account Delegation