Counter

The following example implements a counter which is able to:

• Increment the count by 1
• Decrement the count by 1
• Retrieve the value of the counter

ABI

To create a counter we must define an ABI which exposes methods that manipulate the count and retrieve its value. Since we are handling storage we must provide storage annotations on the functions.

abi Counter {
    #[storage(read, write)]
    fn increment();

    #[storage(read, write)]
    fn decrement();

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

Implementation

We initialize a count in storage with the value of zero and implement methods to increment & decrement the count by one and return the value.

storage {
    counter: u64 = 0,
}

impl Counter for Contract {
    #[storage(read, write)]
    fn increment() {
        storage.counter.write(storage.counter.read() + 1);
    }

    #[storage(read, write)]
    fn decrement() {
        storage.counter.write(storage.counter.read() - 1);
    }

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