https://sway-playground.org/?ref=fuel-labs.ghost.io

contract;

abi TestContract {
#[storage(read, write)]
fn increment_counter(amount: u64) -> u64;

#[storage(read)]
fn get_counter() -> u64;

}

storage {
counter: u64 = 0,
}

impl TestContract for Contract {
#[storage(read, write)]
fn increment_counter(amount: u64) -> u64 {
let incremented = storage.counter.read() + amount;
storage.counter.write(incremented);
incremented
}

#[storage(read)]
fn get_counter() -> u64 {
    storage.counter.read()