Counter

The following is a simple example of a contract which implements a counter. Both the initialize_counter() and increment_counter() ABI methods return the currently set value.

forc template --template-name counter my_counter_project

contract;

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

storage {
    counter: u64 = 0,
}

impl TestContract for Contract {
    #[storage(write)]
    fn initialize_counter(value: u64) -> u64 {
        storage.counter = value;
        value
    }

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