All contracts in Fuel can mint and burn their own native asset. Contracts can also receive and transfer any native asset including their own. Internal balances of all native assets pushed through calls or minted by the contract are tracked by the FuelVM and can be queried at any point using the balance_of function from the std library. Therefore, there is no need for any manual accounting of the contract's balances using persistent storage.
The std library provides handy methods for accessing Fuel's native asset operations.
In this example, we show a basic liquidity pool contract minting its own native asset LP asset.
contract;
use std::{
asset::{
mint_to,
transfer,
},
call_frames::msg_asset_id,
constants::DEFAULT_SUB_ID,
context::msg_amount,
hash::*,
};
abi LiquidityPool {
fn deposit(recipient: Address);
fn withdraw(recipient: Address);
}
const BASE_ASSET: AssetId = AssetId::from(0x9ae5b658754e096e4d681c548daf46354495a437cc61492599e33fc64dcdc30c);
impl LiquidityPool for Contract {
fn deposit(recipient: Address) {
assert(msg_asset_id() == BASE_ASSET);
assert(msg_amount() > 0);
// Mint two times the amount.
let amount_to_mint = msg_amount() * 2;
// Mint some LP assets based upon the amount of the base asset.
mint_to(Identity::Address(recipient), DEFAULT_SUB_ID, amount_to_mint);
}
fn withdraw(recipient: Address) {
let asset_id = AssetId::default();
assert(msg_asset_id() == asset_id);
assert(msg_amount() > 0);
// Amount to withdraw.
let amount_to_transfer = msg_amount() / 2;
// Transfer base asset to recipient.
transfer(Identity::Address(recipient), BASE_ASSET, amount_to_transfer);
}
}